staging: drm/imx: ipu-dc: signedness bug in ipu_dc_init_sync()

"map" needs to be signed for the error handling to work.  In the success
case then it holds a small non-negative value.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Acked-by: Marek Vasut <marex@denx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/imx-drm/ipu-v3/ipu-dc.c

@@ -161,14 +161,15 @@ int ipu_dc_init_sync(struct ipu_dc *dc, struct ipu_di *di, bool interlaced,
 		u32 pixel_fmt, u32 width)
 {
 	struct ipu_dc_priv *priv = dc->priv;
-	u32 reg = 0, map;
+	u32 reg = 0;
+	int map;
 
 	dc->di = ipu_di_get_num(di);
 
 	map = ipu_pixfmt_to_map(pixel_fmt);
 	if (map < 0) {
 		dev_dbg(priv->dev, "IPU_DISP: No MAP\n");
-		return -EINVAL;
+		return map;
 	}
 
 	if (interlaced) {