Fix pre-mounted Btrfs subvolumes root detection

Author: codefiles

archinstall/lib/disk/device_handler.py

@@ -244,7 +244,7 @@ def get_btrfs_info(
 			# expected output format:
 			# ID 257 gen 8 top level 5 path @home
 			name = Path(line.split(' ')[-1])
-			sub_vol_mountpoint = btrfs_subvol_info.get(name, None)
+			sub_vol_mountpoint = btrfs_subvol_info.get('/' / name, None)
 			subvol_infos.append(_BtrfsSubvolumeInfo(name, sub_vol_mountpoint))
 
 		if not lsblk_info.mountpoint: