Bluetooth: Audio: Shell: Fix context for the audio shell

The context had a bug where if GMAP was enabled, the context
was only BT_AUDIO_CONTEXT_TYPE_GAME.

The context should also (per BAP spec requirement) contain the
BT_AUDIO_CONTEXT_TYPE_UNSPECIFIED context.

Signed-off-by: Emil Gydesen <emil.gydesen@nordicsemi.no>