drm/panel: himax-hx83102: Check for errors on the NOP in prepare()

The mipi_dsi_dcs_nop() function returns an error but we weren't
checking it in hx83102_prepare(). Add a check. This is highly unlikely
to matter in practice. If the NOP failed then likely later MIPI
commands would fail too.

Found by code inspection.

Fixes: 0ef94554 ("drm/panel: himax-hx83102: Break out as separate driver")
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20240517143643.7.I3fae28745bf2cacd8dac04d7a06daea50e233f46@changeidSigned-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240517143643.7.I3fae28745bf2cacd8dac04d7a06daea50e233f46@changeid

drivers/gpu/drm/panel/panel-himax-hx83102.c

@@ -547,7 +547,11 @@ static int hx83102_prepare(struct drm_panel *panel)
 
 	usleep_range(10000, 11000);
 
-	mipi_dsi_dcs_nop(ctx->dsi);
+	ret = mipi_dsi_dcs_nop(ctx->dsi);
+	if (ret < 0) {
+		dev_err(dev, "Failed to send NOP: %d\n", ret);
+		goto poweroff;
+	}
 	usleep_range(1000, 2000);
 
 	gpiod_set_value(ctx->enable_gpio, 1);