btrfs: let can_allocate_chunk return error

[ Upstream commit bb9950d3 ]

For the later patch, convert the return type from bool to int and return
errors. No functional changes.

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