bcachefs: print op->nonce on data update inconsistency

"nonce inconstancy" is popping up again, causing us to go emergency
read-only.

This one looks less serious, i.e. specific to the encryption path and
not indicative of a data corruption bug. But we'll need more info to
track it down.

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