ALSA: hiface: Fix M2Tech hiFace driver sampling rate change

Sampling rate changes after first set one are not reflected to the
hardware, while driver and ALSA think the rate has been changed.

Fix the problem by properly stopping the interface at the beginning of
prepare call, allowing new rate to be set to the hardware. This keeps
the hardware in sync with the driver.

Signed-off-by: Jussi Laako <jussi@sonarnerd.net>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>