btrfs: factor out chunk_allocation_failed() for extent allocation

Factor out chunk_allocation_failed() from
find_free_extent_update_loop().  This function is called when it failed
to allocate a chunk. The function can modify "ffe_ctl->loop" and return
0 to continue with the next stage.  Or, it can return -ENOSPC to give up
here.

Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>