fs/bio-integrity.c: remove duplicated code

fs/bio-integrity.c: remove duplicated code

Most code of function bio_integrity_verify and bio_integrity_generate is
the same, so introduce a common function bio_integrity_generate_verify()
to remove the reduplicate code.

Signed-off-by: Gu Zheng <guz.fnst@cn.fujitsu.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>