disk: use cxt.label.name to dtect disk type in get_efi_partition

Use cxt.label.name instead of cxt.label to identify if the disk is
GPT or MBR. This way is more used in other parts of the codebase.

src/utils/disk.py

@@ -105,7 +105,7 @@ def get_efi_partition(disknum, enforce_gpt):
     disk = get_disks()[disk_index]
     cxt = fdisk.Context(f'/dev/{disk}')
 
-    if enforce_gpt and cxt.label == fdisk.FDISK_DISKLABEL_DOS:
+    if enforce_gpt and cxt.label.name == 'dos':
         raise OgError(f'Windows EFI partition requires GPT partition scheme, but /dev/{disk} has DOS partition scheme')
 
     logging.info('Searching EFI partition...')