ALSA: emu10k1: properly assert E-MU FPGA access constaints

ALSA: emu10k1: properly assert E-MU FPGA access constaints

Assert the validity of the registers and values, as them being out of
range would indicate an error in the driver. Consequently, don't bother
returning error codes; they were ignored everywhere anyway.

Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Link: https://lore.kernel.org/r/20230421141006.1005539-1-oswald.buddenhagen@gmx.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>