btrfs: extend btrfs_leaf_check to return btrfs_tree_block_status

Instead of blanket returning -EUCLEAN for all the failures in
btrfs_check_leaf, use btrfs_tree_block_status and return the appropriate
status for each failure.  Rename the helper to __btrfs_check_leaf and
then make a wrapper of btrfs_check_leaf that will return -EUCLEAN to
non-clean error codes.  This will allow us to have the
__btrfs_check_leaf variant in btrfs-progs while keeping the behavior in
the kernel consistent.

Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>