ALSA: snd-atmel-ac97c: do a proper reset of the external codec

This patch will enable the AC97C before resetting the external codec,
leaving the AC97C disabled will result in floating I/O lines that can
affect the reset procedure.

Signed-off-by: Hans-Christian Egtvedt <hans-christian.egtvedt@atmel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>