bcachefs: Always check for invalid bkeys in main commit path

bcachefs: Always check for invalid bkeys in main commit path

Previously, we would check for invalid bkeys at transaction commit time,
but only if CONFIG_BCACHEFS_DEBUG=y.

This check is important enough to always be on - it appears there's been
corruption making it into the journal that would have been caught by it.

Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>