bcachefs: bch2_alloc_write() should be writing for all devices

bcachefs: bch2_alloc_write() should be writing for all devices

Alloc info isn't stored on a particular device, it makes no sense to
only be writing it out for rw members - this was causing fsck to not fix
alloc info errors, oops.

Also, make sure we write out alloc info in other repair paths.

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