bcachefs: bch2_write_op_error() now prints info about data update

bcachefs: bch2_write_op_error() now prints info about data update

A user has been seeing the "error verifying existing checksum while
rewriting existing data (memory corruption?)" error.

This generally indicates a hardware issue (and that may be the case
here), but it might also indicate a bug, in which case we need more
information to look for patterns.

Reported-by: Roland Vet <vet.roland@protonmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>