Android Mute and FastForward keys mapped wrong

KEYCODE_MEDIA_FAST_FORWARD is mapped to Qt::Key_Forward,
which undoes Back. I believe the best match in Qt would be
Qt::Key_AudioForward which is also mapped by XCB from
XF86XK_AudioForward /* fast-forward audio track    */

KEYCODE_MUTE is mapped to Qt::Key_Volume_Mute, but the mute button is
for muting the microphone, the volume mute is called
KEYCODE_VOLUME_MUTE.

Change-Id: Id0b78c9bde78faef1f5d31019693e6c466941d70
Reviewed-by: BogDan Vatra <bogdan@kde.org>