ALSA: hda: fix a mask for unsolicited event tags

Response tag only occupies 6 bits, not 7. This bug is harmless, since
the value has just been shifted to the right by 26 bits, so this is
only a cosmetic fix.

Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@linux.intel.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>