bcachefs: Don't run triggers in fix_reflink_p_key()

bcachefs: Don't run triggers in fix_reflink_p_key()

It seems some users have reflink pointers which span many indirect
extents, from a short window in time when merging of reflink pointers
was allowed.

Now, we're seeing transaction path overflows in fix_reflink_p(), the
code path to clear out the reflink_p fields now used for front/back pad
- but, we don't actually need to be running triggers in that path, which
is an easy partial fix.

Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>