[ALSA] WM9713 modem detection

AC97 Codec
This patch fixes a problem whereby the WM9713 has modem functionality
incorrectly detected after an AC97 cold reset.

Changes:-

  o Cleared AC97_SCAP_MODEM in wm9713 scaps

Signed-off-by: Liam Girdwood <liam.girdwood@wolfsonmicro.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>