refs/files: remove useless indirection

refs/files: remove useless indirection

The function `files_fsck_refs()` only has a single callsite and forwards
all of its arguments as-is, so it's basically a useless indirection.
Inline the function call.

While at it, also remove the bitwise or that we have for return values.
We don't really want to or them at all, but rather just want to return
an error in case either of the functions has failed.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>