Btrfs-progs: fsck: fix wrong return value in check_block()

Btrfs-progs: fsck: fix wrong return value in check_block()

We found btrfsck will output backrefs mismatch while the filesystem
is defenitely ok.

The problem is that check_block() don't return right value,which
makes btrfsck won't walk all tree blocks thus we don't get a consistent
filesystem, we will fail to check extent refs etc.

Reported-by: Gui Hecheng <guihc.fnst@cn.fujitsu.com>
Signed-off-by: Wang Shilong <wangsl.fnst@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Chris Mason <clm@fb.com>