[ALSA] Fix WM9705 AC97 patch build error

This patch fixes a build error (introduced by me) in ac97_patch.c wrt
WM9705 touchscreen.
 o Removed spurious '3D' from character after |= operation (0x3D is
ASCII for '=')

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