RDMA/verbs: Simplify modify QP check

All callers to ib_modify_qp_is_ok() provides enum ib_qp_state
makes the checks of out-of-scope redundant. Let's remove them
together with updating function signature to return boolean result.

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