net: caif: fix erroneous return value

The cfrfml_receive() function might return positive value EPROTO

Signed-off-by: Anton Protopopov <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

net/caif/cfrfml.c

···
 		tmppkt = NULL;
 
 		/* Verify that length is correct */
-		err = EPROTO;
+		err = -EPROTO;
 		if (rfml->pdu_size != cfpkt_getlen(pkt) - RFM_HEAD_SIZE + 1)
 			goto out;
 	}