[ALSA] ASoC: sh: improve generated code for HAC module (AC97)

Change loops in ac97_read/write functions to count down to zero
rather than up. Gcc will then use the 'dt' (decrement-and-test) op
instead of an increment/compare op-pair.

Signed-off-by: Manuel Lauss <mano@roarinelk.homelinux.net>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@perex.cz>