bcachefs: Fix move_extent_fail counter

fail counters need to be events, not numbers of sectors - or the
calculations the tests use for determining if we've had too many
slowpath events don't work.

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

fs/bcachefs/data_update.c

@@ -374,7 +374,7 @@ nowork:
 				     &m->ctxt->stats->sectors_raced);
 		}
 
-		this_cpu_add(c->counters[BCH_COUNTER_move_extent_fail], new->k.size);
+		this_cpu_inc(c->counters[BCH_COUNTER_move_extent_fail]);
 
 		bch2_btree_iter_advance(&iter);
 		goto next;