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.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>