usb: image: mdc800: Remove redundant assignment to variable retval

The variable retval is being assigned a value that is not being read
and is being re-assigned a new value a couple of statements later.
The assignment is redundant and can be removed.

Cleans up clang scan warning:
drivers/usb/image/mdc800.c:634:2: warning: Value stored to 'retval'
is never read [deadcode.DeadStores]

Signed-off-by: Colin Ian King <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/image/mdc800.c

···
 	mdc800->camera_busy=0;
 	mdc800->camera_request_ready=0;
 
-	retval=0;
 	mdc800->irq_urb->dev = mdc800->dev;
 	retval = usb_submit_urb (mdc800->irq_urb, GFP_KERNEL);
 	if (retval) {