drm/mipi-dsi: Fix theoretical int overflow in mipi_dsi_generic_write_seq()

The mipi_dsi_generic_write_seq() macro makes a call to
mipi_dsi_generic_write() which returns a type ssize_t. The macro then
stores it in an int and checks to see if it's negative. This could
theoretically be a problem if "ssize_t" is larger than "int".

To see the issue, imagine that "ssize_t" is 32-bits and "int" is
16-bits, you could see a problem if there was some code out there that
looked like:

  mipi_dsi_generic_write_seq(dsi, <32768 bytes as arguments>);

...since we'd get back that 32768 bytes were transferred and 32768
stored in a 16-bit int would look negative.

Though there are no callsites where we'd actually hit this (even if
"int" was only 16-bit), it's cleaner to make the types match so let's
fix it.

Fixes: a9015ce5 ("drm/mipi-dsi: Add a mipi_dsi_dcs_write_seq() macro")
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://lore.kernel.org/r/20240514102056.v5.2.Iadb65b8add19ed3ae3ed6425011beb97e380a912@changeidSigned-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240514102056.v5.2.Iadb65b8add19ed3ae3ed6425011beb97e380a912@changeid

include/drm/drm_mipi_dsi.h

@@ -314,17 +314,17 @@ int mipi_dsi_dcs_get_display_brightness_large(struct mipi_dsi_device *dsi,
  * @dsi: DSI peripheral device
  * @seq: buffer containing the payload
  */
-#define mipi_dsi_generic_write_seq(dsi, seq...)                                \
-	do {                                                                   \
-		static const u8 d[] = { seq };                                 \
-		struct device *dev = &dsi->dev;                                \
-		int ret;                                                       \
-		ret = mipi_dsi_generic_write(dsi, d, ARRAY_SIZE(d));           \
-		if (ret < 0) {                                                 \
-			dev_err_ratelimited(dev, "transmit data failed: %d\n", \
-					    ret);                              \
-			return ret;                                            \
-		}                                                              \
+#define mipi_dsi_generic_write_seq(dsi, seq...)                                 \
+	do {                                                                    \
+		static const u8 d[] = { seq };                                  \
+		struct device *dev = &dsi->dev;                                 \
+		ssize_t ret;                                                    \
+		ret = mipi_dsi_generic_write(dsi, d, ARRAY_SIZE(d));            \
+		if (ret < 0) {                                                  \
+			dev_err_ratelimited(dev, "transmit data failed: %zd\n", \
+					    ret);                               \
+			return ret;                                             \
+		}                                                               \
 	} while (0)
 
 /**