usb: cdc-wdm: remove logically dead code

Remove logically dead code.
'cntr' is always equal to zero when the following line of code is executed:
rv = cntr ? cntr : -EAGAIN;

Addresses-Coverity-ID: 113227
Signed-off-by: NGustavo A. R. Silva <garsilva@embeddedor.com>
Acked-by: NOliver Neukum <oneukum@suse.com>
Reviewed-by: NPeter Senna Tschudin <peter.senna@gmail.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/class/cdc-wdm.c

@@ -531,7 +531,7 @@ static ssize_t wdm_read
 		i++;
 		if (file->f_flags & O_NONBLOCK) {
 			if (!test_bit(WDM_READ, &desc->flags)) {
-				rv = cntr ? cntr : -EAGAIN;
+				rv = -EAGAIN;
 				goto err;
 			}
 			rv = 0;