btrfs: remove pointless label and goto from unpin_extent_range()

btrfs: remove pointless label and goto from unpin_extent_range()

There's no need to have an 'out' label and jump there in case we can
not find a block group. We can simply return directly since there are no
resources to release, removing the need for the label and the 'ret'
variable.

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>