btrfs: sysfs: fix direct super block member reads

The following sysfs entries are reading super block member directly,
which can have a different endian and cause wrong values:

- sys/fs/btrfs/<uuid>/nodesize
- sys/fs/btrfs/<uuid>/sectorsize
- sys/fs/btrfs/<uuid>/clone_alignment

Thankfully those values (nodesize and sectorsize) are always aligned
inside the btrfs_super_block, so it won't trigger unaligned read errors,
just endian problems.

Fix them by using the native cached members instead.

Fixes: df93589a1737 ("btrfs: export more from FS_INFO to sysfs")
CC: [e-mail]
Reviewed-by: Naohiro Aota <[e-mail]>
Reviewed-by: Johannes Thumshirn <[e-mail]>
Signed-off-by: Qu Wenruo <[e-mail]>
Reviewed-by: David Sterba <[e-mail]>
Signed-off-by: David Sterba <[e-mail]>

fs/btrfs/sysfs.c

···
 {
 	struct btrfs_fs_info *fs_info = to_fs_info(kobj);
 
-	return sysfs_emit(buf, "%u\n", fs_info->super_copy->nodesize);
+	return sysfs_emit(buf, "%u\n", fs_info->nodesize);
 }
 
 BTRFS_ATTR(, nodesize, btrfs_nodesize_show);
···
 {
 	struct btrfs_fs_info *fs_info = to_fs_info(kobj);
 
-	return sysfs_emit(buf, "%u\n", fs_info->super_copy->sectorsize);
+	return sysfs_emit(buf, "%u\n", fs_info->sectorsize);
 }
 
 BTRFS_ATTR(, sectorsize, btrfs_sectorsize_show);
···
 {
 	struct btrfs_fs_info *fs_info = to_fs_info(kobj);
 
-	return sysfs_emit(buf, "%u\n", fs_info->super_copy->sectorsize);
+	return sysfs_emit(buf, "%u\n", fs_info->sectorsize);
 }
 
 BTRFS_ATTR(, clone_alignment, btrfs_clone_alignment_show);