mlx5ib: Fix XRC QP support after introducing extended atomic.

Extended atomics are supported with RC and XRC QP types, but Linux commit
a60109dc9a95 added an unneeded check to to_mlx5_access_flags().
This broke XRC QPs.

The following ib_atomic_bw invocation over XRC reproduces the issue:
ib_atomic_bw -d mlx5_1 --connection=XRC --atomic_type=FETCH_AND_ADD

It is safe to remove such checks because the QP type was already checked
in ib_modify_qp_is_ok(), which was previously called from
mlx5_ib_modify_qp().

Linux commit:
13f8d9c16693afb908ead3d2a758adbe6a79eccd

Reviewed by: kib
Sponsored by: Mellanox Technologies // NVIDIA Networking

(cherry picked from commit cf88b86e4954215eb447729042dab8dea722c044)