ALSA: emu10k1: fix+optimize E-MU stereo capture DSP code

ALSA: emu10k1: fix+optimize E-MU stereo capture DSP code

Presumably, JDC added the seemingly superfluous indirection over the
temporary register because without it he'd get only zero readings.
However, switching the X and Y operands (or using EMU32 as the A
operand in the temporary load) works just fine. Presumably a DSP bug?

The original code was also actually buggy, though: both channels used
the left volume control.

Signed-off-by: Oswald Buddenhagen <oswald.buddenhagen@gmx.de>
Link: https://lore.kernel.org/r/20230510173917.3073107-4-oswald.buddenhagen@gmx.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>