block: Fix nr_vecs for inline integrity vectors

Commit 9f060e22 changed the way we handle allocations for the
integrity vectors. When the vectors are inline there is no associated
slab and consequently bvec_nr_vecs() returns 0. Ensure that we check
against BIP_INLINE_VECS in that case.

Reported-by: David Milburn <dmilburn@redhat.com>
Tested-by: David Milburn <dmilburn@redhat.com>
Cc: stable@vger.kernel.org # v3.10+
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Jens Axboe <axboe@fb.com>