The gc_gens_pos is used to show the status of bucket gen gc.
There is no need to assign write permissions for this attribute.
Here we can use read_attribute helper to define this attribute.
```
[Before]
$ ll internal/gc_gens_pos
-rw-r--r-- 1 root root 4096 Oct 28 15:27 internal/gc_gens_pos
[After]
$ ll internal/gc_gens_pos
-r--r--r-- 1 root root 4096 Oct 28 17:27 internal/gc_gens_pos
```
Fixes:
ac516d0e7db7 ("bcachefs: Add the status of bucket gen gc to sysfs")
Signed-off-by: Hongbo Li <lihongbo22@huawei.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
write_attribute(trigger_btree_cache_shrink);
write_attribute(trigger_btree_key_cache_shrink);
write_attribute(trigger_freelist_wakeup);
-rw_attribute(gc_gens_pos);
+read_attribute(gc_gens_pos);
read_attribute(uuid);
read_attribute(minor);