We're using the WpReserveDevice's name as key in the hash table, so we
must update the key as well when we replace an item in the hashtable -
the old device (and its name) will be released.

The side-effect of this is that the *third* device with an identical
name will no longer replace the previous device. This results in the
following sequence:

- dev1 added: name Audio0
  - dev1 requests name owner Audio0
- dev2 added: name Audio0
  - replace dev1 in the hashtable
     - dev1 emits "release" signal
     - dev1 unowns the Audio0 name
  - dev2 requests name owner Audio0
- dev3 added: name Audio0
  - adds to the hashtable because the existing key is now undefined
  - dev3 requests name owner Audio0
     - error, you cannot request ownership for the same name twice

Fixes #93