IB/mlx5: Remove MTT access mode from umr flags helper function

get_umr_flags helper function might be used for types of access modes
other than ACCESS_MODE_MTT, such as ACCESS_MODE_KLM.  So remove it from
helper, and callers will add their own access mode flag.

This commit does not add/change functionality.

Signed-off-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>