V4L/DVB (5019): Fix the frame->grabstate update in read() entry point.

The Coverity checker spotted that in usbvision_v4l2_read(), the variable
"frmx" is never assigned any value different from -1, but it's used an 
an array index in "usbvision->frame[frmx]".
Thanks to Adrian Bunk <bunk@stusta.de> for warning about that.
Signed-off-by: Thierry MERLE <thierry.merle@free.fr>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>

drivers/media/video/usbvision/usbvision-video.c

@@ -1080,7 +1080,6 @@ static ssize_t usbvision_v4l2_read(struct file *file, char *buf,
 	int noblock = file->f_flags & O_NONBLOCK;
 	unsigned long lock_flags;
 
-	int frmx = -1;
 	int ret,i;
 	struct usbvision_frame *frame;
 
@@ -1155,7 +1154,7 @@ static ssize_t usbvision_v4l2_read(struct file *file, char *buf,
 		frame->bytes_read = 0;
 
 		/* Mark it as available to be used again. */
-		usbvision->frame[frmx].grabstate = FrameState_Unused;
+		frame->grabstate = FrameState_Unused;
 /* 	} */
 
 	return count;