btrfs: subpage: fix the bitmap dump of the locked flags

btrfs: subpage: fix the bitmap dump of the locked flags

We're dumping the locked bitmap into the @checked_bitmap variable,
printing incorrect values during debug.

Thankfully even during my development I haven't hit a case where I need
to dump the locked bitmap.  But for the sake of consistency, fix it by
dupping the locked bitmap into @locked_bitmap variable for output.

Fixes: 75258f20fb70 ("btrfs: subpage: dump extra subpage bitmaps for debug")
Reviewed-by: Boris Burkov <boris@bur.io>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>