IB/mlx4: Test return value of calls to ib_get_cached_pkey

In the mlx4_ib_post_send() flow, some functions call ib_get_cached_pkey()
without checking its return value. If ib_get_cached_pkey() returns an
error code, these functions should return failure.

Fixes: 1ffeb2eb ("IB/mlx4: SR-IOV IB context objects and proxy/tunnel SQP support")
Fixes: 225c7b1f ("IB/mlx4: Add a driver Mellanox ConnectX InfiniBand adapters")
Fixes: e622f2f4 ("IB: split struct ib_send_wr")
Link: https://lore.kernel.org/r/20200426075921.130074-1-leon@kernel.org


Signed-off-by: Jack Morgenstein <jackm@dev.mellanox.co.il>
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>