quota: remove unneeded return value of register_quota_format

The register_quota_format always returns 0, simply remove unneeded return
value.

Link: https://patch.msgid.link/20240715130534.2112678-3-shikemeng@huaweicloud.com


Signed-off-by: Kemeng Shi <shikemeng@huaweicloud.com>
Reviewed-by: Joseph Qi <joseph.qi@linux.alibaba.com>
Signed-off-by: Jan Kara <jack@suse.cz>