* Don't attempt to use device reservation when card_to_num() mapping
   has failed. In case of card_to_num() failures, "Audio-1" device
   was reserved on start but not released on stop. This was causing
   next start to fail with out of memory error, and since previous
   commit, with "A handler is already registered for
   /org/freedesktop/ReserveDevice1/Audio-1" error.
 * In case of playback device reservation failure, release the
   capture device
 * Remove unused fReservedCaptureDevice and fReservedPlaybackDevice
   data members of the JackAlsaDriver class