[media] usbvision-core: fix a warning

drivers/media/usb/usbvision/usbvision-core.c:1749:2: warning: comparison of unsigned expression < 0 is always false [-Wtype-limits]
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/usb/usbvision/usbvision.h

@@ -167,7 +167,7 @@ enum {
 
 /* This macro restricts an int variable to an inclusive range */
 #define RESTRICT_TO_RANGE(v, mi, ma) \
-	{ if ((v) < (mi)) (v) = (mi); else if ((v) > (ma)) (v) = (ma); }
+	{ if (((int)v) < (mi)) (v) = (mi); else if ((v) > (ma)) (v) = (ma); }
 
 /*
  * We use macros to do YUV -> RGB conversion because this is