ALSA: asihpi - Fix format validity check.

Sharing and not reinitialising static pcm_hardware struct resulted in
stream format validity flags being incorrectly shared between cards.
Fix and clarify by declaring locally and initialising in the open functions.

Signed-off-by: Eliot Blennerhassett <eblennerhassett@audioscience.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>