RDMA/mlx4: Remove gfp_mask argument from acquire_group call

All callers of acquire_group() passed the same gfp_mask to it
and it is safe to remove it.

Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Reviewed-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>