ALSA: emu10k1: track loss of external clock on E-MU cards

ALSA: emu10k1: track loss of external clock on E-MU cards
85;95;0c
This uses IRQs to track spontaneous changes to the word clock source
register.

FWIW, that this can happen in the first place is the reason why it is
futile to lock the clock source mixer setting while the device is open -
we can't consistently control the rate anyway. Though arguably, we
should reset any open streams when that happens, as they become
corrupted anyway.

Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Link: https://lore.kernel.org/r/20230715160738.326832-1-oswald.buddenhagen@gmx.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>