Add Vol+/Vol-/Mute panel button mappings for iMON VFD HID OEM v1.2.
This version differs in the codes that generate the
KEY_VOLUMEUP, KEY_VOLUMEDOWN and KEY_MUTE events.
Signed-off-by: Alessandro Baldi <baldovic@virgilio.it> Signed-off-by: Sean Young <sean@mess.org>