net/mlx4: Assign boolean values to a bool variable

Fix the following coccinelle warnings:

./drivers/net/ethernet/mellanox/mlx4/en_rx.c:687:1-17: WARNING: Assignment of 0/1 to bool variable
Reported-by: Tosk Robot <tencent_os_robot@tencent.com>
Signed-off-by: Kaixu Xia <kaixuxia@tencent.com>
Reviewed-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://lore.kernel.org/r/1604732038-6057-1-git-send-email-kaixuxia@tencent.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/mellanox/mlx4/en_rx.c

@@ -684,7 +684,7 @@ int mlx4_en_process_rx_cq(struct net_device *dev, struct mlx4_en_cq *cq, int bud
 	xdp_prog = rcu_dereference(ring->xdp_prog);
 	xdp.rxq = &ring->xdp_rxq;
 	xdp.frame_sz = priv->frag_info[0].frag_stride;
-	doorbell_pending = 0;
+	doorbell_pending = false;
 
 	/* We assume a 1:1 mapping between CQEs and Rx descriptors, so Rx
 	 * descriptor offset can be deduced from the CQE index instead of