bcachefs: Fix recovery when forced to use JSET_NO_FLUSH journal entry

When we didn't find anything in the journal that we'd like to use, and
we're forced to use whatever we can find - that entry will have been a
JSET_NO_FLUSH entry with a garbage last_seq value, since it's not
normally used.

Initialize it to something sane, for bch2_fs_journal_start().
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/recovery.c

@@ -735,6 +735,13 @@ int bch2_fs_recovery(struct bch_fs *c)
 				if (*i) {
 					last_journal_entry = &(*i)->j;
 					(*i)->ignore = false;
+					/*
+					 * This was probably a NO_FLUSH entry,
+					 * so last_seq was garbage - but we know
+					 * we're only using a single journal
+					 * entry, set it here:
+					 */
+					(*i)->j.last_seq = (*i)->j.seq;
 					break;
 				}
 		}