udiskie: Also list read-only filesystems

In case the media contains a read-only copy of a backup and we need to restore
from it.

Reviewed-by: James Valleroy <jvalleroy@mailbox.org>

plinth/modules/udiskie/udisks2.py

@@ -47,8 +47,7 @@ def list_devices():
 
         block = obj.get_block()
         if block.props.id_usage != 'filesystem' or \
-           block.props.hint_system or \
-           block.props.read_only:
+           block.props.hint_system:
             continue
 
         device_name = block.props.device