IB/mlx4: Fix a sparse endianness warning

Fix the following warning for the mlx4 driver:

    $ make M=drivers/infiniband C=2 CF=-D__CHECK_ENDIAN__
    drivers/infiniband/hw/mlx4/qp.c:1885:31: warning: restricted __be16 degrades to integer

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Roland Dreier <roland@purestorage.com>
diff --git a/drivers/infiniband/hw/mlx4/qp.c b/drivers/infiniband/hw/mlx4/qp.c
index d8f4d1f..7499325 100644
--- a/drivers/infiniband/hw/mlx4/qp.c
+++ b/drivers/infiniband/hw/mlx4/qp.c
@@ -1882,7 +1882,7 @@
 				return err;
 		}
 
-		if (ah->av.eth.vlan != 0xffff) {
+		if (ah->av.eth.vlan != cpu_to_be16(0xffff)) {
 			vlan = be16_to_cpu(ah->av.eth.vlan) & 0x0fff;
 			is_vlan = 1;
 		}