V4L/DVB (7734): em28xx: copy and paste error in em28xx_init_isoc

Fixes a copy and paste error in check of kzalloc return value. The check block
was copied from the previous allocation but the variable wasn't exchanged.
Signed-off-by: NMauro Carvalho Chehab <mchehab@infradead.org>

drivers/media/video/em28xx/em28xx-core.c

@@ -650,7 +650,7 @@ int em28xx_init_isoc(struct em28xx *dev, int max_packets,
 
 	dev->isoc_ctl.transfer_buffer = kzalloc(sizeof(void *)*num_bufs,
 					      GFP_KERNEL);
-	if (!dev->isoc_ctl.urb) {
+	if (!dev->isoc_ctl.transfer_buffer) {
 		em28xx_errdev("cannot allocate memory for usbtransfer\n");
 		kfree(dev->isoc_ctl.urb);
 		return -ENOMEM;