drm/bridge: anx7625: Fix overflow issue on reading EDID

The length of EDID block can be longer than 256 bytes, so we should use
`int` instead of `u8` for the `edid_pos` variable.

Fixes: 8bdfc5da ("drm/bridge: anx7625: Add anx7625 MIPI DSI/DPI to DP")
Signed-off-by: Pin-Yen Lin <treapking@chromium.org>
Reviewed-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220210103827.402436-1-treapking@chromium.org

drivers/gpu/drm/bridge/analogix/anx7625.c

@@ -1109,7 +1109,8 @@ static int segments_edid_read(struct anx7625_data *ctx,
 static int sp_tx_edid_read(struct anx7625_data *ctx,
 			   u8 *pedid_blocks_buf)
 {
-	u8 offset, edid_pos;
+	u8 offset;
+	int edid_pos;
 	int count, blocks_num;
 	u8 pblock_buf[MAX_DPCD_BUFFER_SIZE];
 	u8 i, j;