[media] gsc-m2m: Use an unsigned data type for a variable

The data type "int" was used by the variable "ret" in the
gsc_m2m_poll() function despite of the aspect that the type "unsigned int"
will usually be needed for the return value from a call of the
v4l2_m2m_poll() function.
Improve this implementation detail by addition of the type modifier then.

This issue was detected by using the Coccinelle software.
Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>

drivers/media/platform/exynos-gsc/gsc-m2m.c

@@ -700,7 +700,7 @@ static unsigned int gsc_m2m_poll(struct file *file,
 {
 	struct gsc_ctx *ctx = fh_to_ctx(file->private_data);
 	struct gsc_dev *gsc = ctx->gsc_dev;
-	int ret;
+	unsigned int ret;
 
 	if (mutex_lock_interruptible(&gsc->lock))
 		return -ERESTARTSYS;