block/bio-integrity: don't free 'buf' if bio_integrity_add_page() failed

commit e7bf90e5 ("block/bio-integrity: fix a memory leak bug") added
a kfree() for 'buf' if bio_integrity_add_page() returns '0'. However,
the object will be freed in bio_integrity_free() since 'bio->bi_opf' and
'bio->bi_integrity' were set previousy in bio_integrity_alloc().

Fixes: commit e7bf90e5 ("block/bio-integrity: fix a memory leak bug")
Signed-off-by: yu kuai <yukuai3@huawei.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Bob Liu <bob.liu@oracle.com>
Acked-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>