xfs: Fix leak of discard bio

The bio describing discard operation is allocated by
__blkdev_issue_discard() which returns us a reference to it. That
reference is never released and thus we leak this bio. Drop the bio
reference once it completes in xlog_discard_endio().

CC: stable@vger.kernel.org
Fixes: 4560e78fSigned-off-by: NJan Kara <jack@suse.cz>
Reviewed-by: NDarrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>

fs/xfs/xfs_log_cil.c

@@ -539,6 +539,7 @@ xlog_discard_endio(
 
 	INIT_WORK(&ctx->discard_endio_work, xlog_discard_endio_work);
 	queue_work(xfs_discard_wq, &ctx->discard_endio_work);
+	bio_put(bio);
 }
 
 static void