storage: fix crash when coming back from FS screen

In order to fix a screen not refreshing issue, the following patch
changed the return type of make_ui from an object to a callable in the
storage controller:

414a2235 storage: fix screen sometimes not refreshing after slow probing

The storage controller is the only one that reuses its make_ui()
coroutine internally. Unfortunately, the code that calls await make_ui()
was not updated in the storage controller.

Signed-off-by: Olivier Gayot <olivier.gayot@canonical.com>

subiquity/client/controllers/filesystem.py

@@ -254,7 +254,7 @@ class FilesystemController(SubiquityTuiController, FilesystemManipulator):
         self.app.aio_loop.create_task(self._guided_choice(choice))
 
     async def _guided(self):
-        self.ui.set_body(await self.make_ui())
+        self.ui.set_body((await self.make_ui())())
 
     def guided(self):
         self.app.aio_loop.create_task(self._guided())