drm/bridge: it6505: Fix the read buffer array bound

The size of read_buf is READ_BUFFER_SIZE (200), so we can't access it
with read_buf + PAGE_SIZE (4096). Extend the READ_BUFFER_SIZE to 400 and
set the end position to read_buf + READ_BUFFER_SIZE.

Fixes: b5c84a9e ("drm/bridge: add it6505 driver")
Reported-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220228081421.1504213-1-hsinyi@chromium.org

drivers/gpu/drm/bridge/ite-it6505.c

@@ -289,7 +289,7 @@
 #define WORD_LENGTH_20BIT 2
 #define WORD_LENGTH_24BIT 3
 #define DEBUGFS_DIR_NAME "it6505-debugfs"
-#define READ_BUFFER_SIZE 200
+#define READ_BUFFER_SIZE 400
 
 /* Vendor option */
 #define HDCP_DESIRED 1
@@ -3074,7 +3074,7 @@ static ssize_t receive_timing_debugfs_show(struct file *file, char __user *buf,
 	struct it6505 *it6505 = file->private_data;
 	struct drm_display_mode *vid = &it6505->video_info;
 	u8 read_buf[READ_BUFFER_SIZE];
-	u8 *str = read_buf, *end = read_buf + PAGE_SIZE;
+	u8 *str = read_buf, *end = read_buf + READ_BUFFER_SIZE;
 	ssize_t ret, count;
 
 	if (!it6505)