can: gs_usb: check for kzalloc allocation failure

smatch detected the following issue:
drivers/net/can/usb/gs_usb.c:904 gs_usb_probe() error:
   potential null dereference 'dev'.  (kzalloc returns null)

Add a check for null return from kzalloc and return -ENOMEM

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
diff --git a/drivers/net/can/usb/gs_usb.c b/drivers/net/can/usb/gs_usb.c
index 009acc8..8b4d3e6 100644
--- a/drivers/net/can/usb/gs_usb.c
+++ b/drivers/net/can/usb/gs_usb.c
@@ -901,6 +901,8 @@
 	}
 
 	dev = kzalloc(sizeof(*dev), GFP_KERNEL);
+	if (!dev)
+		return -ENOMEM;
 	init_usb_anchor(&dev->rx_submitted);
 
 	atomic_set(&dev->active_channels, 0);