bcachefs: Don't set BCH_FS_error on transaction restart

This started showing up more when we started logging the error being
corrected in the journal - but __bch2_fsck_err() could return
transaction restarts before that.

Setting BCH_FS_error incorrectly causes recovery passes to not be
cleared, among other issues.

Fixes: b43f7249 ("bcachefs: Log fsck errors in the journal")
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>