ALSA: usb-audio: Add support for Akai MPC Element USB MIDI controller

The Akai MPC Element incorrectly reports its bInterfaceClass as 255, but
otherwise implements the USB MIDI spec correctly.

This adds a quirks-table.h entry which allows the device to be
recognized as a standard USB MIDI device.

Signed-off-by: Paul Bonser <misterpib@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>