[udisks2] Mounts drive twice after unlocking

After unlocking an encrypted drive, I get the following messages:
```
unlocked device /org/freedesktop/UDisks2/block_devices/sdc on /dev/dm-1
mounted device /org/freedesktop/UDisks2/block_devices/dm_2d1 on /run/media/<user>/<drive>
failed to mount device /org/freedesktop/UDisks2/block_devices/dm_2d1: org.freedesktop.UDisks2.Error.AlreadyMounted: Device /dev/dm-1 is already mounted at `/run/media/<user>/<drive>'.
```
The drive mounts correctly.