CAIF: fix sparse warning for caif_usb

This fixes the following sparse warning:
net/caif/caif_usb.c:84:16: warning: symbol 'cfusbl_create' was not
declared. Should it be static?
Signed-off-by: Silviu-Mihai Popescu <silviupopescu1990@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/caif/caif_usb.c

@@ -81,8 +81,8 @@ static void cfusbl_ctrlcmd(struct cflayer *layr, enum caif_ctrlcmd ctrl,
 		layr->up->ctrlcmd(layr->up, ctrl, layr->id);
 }
 
-struct cflayer *cfusbl_create(int phyid, u8 ethaddr[ETH_ALEN],
-					u8 braddr[ETH_ALEN])
+static struct cflayer *cfusbl_create(int phyid, u8 ethaddr[ETH_ALEN],
+				      u8 braddr[ETH_ALEN])
 {
 	struct cfusbl *this = kmalloc(sizeof(struct cfusbl), GFP_ATOMIC);