[ALSA] hdsp - Add 'Sample Clock Source Locking' control

RME HDSP driver
Added 'Sample Clock Source Locking' control.  If this switch is on,
the clock source can't be changed via PCM hw_params API (as sample rate).
This will fix the problem of OSS-emulation, for example.

Signed-off-by: Takashi Iwai <tiwai@suse.de>