ALSA: au88x0: Fix array bounds warning in EQ drivers

ALSA: au88x0: Fix array bounds warning in EQ drivers

In file included from ../sound/pci/au88x0/au8830.c:15:
In function ‘vortex_Eqlzr_SetAllBandsFromActiveCoeffSet’,
../sound/pci/au88x0/au88x0_eq.c:571:9: error: ‘vortex_EqHw_SetRightGainsTarget’ reading 2 bytes from a region of size 0 [-Werror=stringop-overread]
	vortex_EqHw_SetRightGainsTarget(vortex, &(eq->this130[eq->this10]));

Modified the array access in vortex_Eqlzr_SetAllBandsFromActiveCoeffSet() to use pointer arithmetic instead of array indexing.
This resolves a compiler warning that incorrectly flagged a buffer overread when accessing the EQ gain array.
The this130 array has fixed size 20 and the index is safely within bounds, making the original code correct but confusing to static analysis.

Signed-off-by: wangdicheng <wangdicheng@kylinos.cn>
Link: https://patch.msgid.link/20251107024525.38454-1-wangdich9700@163.com
Signed-off-by: Takashi Iwai <tiwai@suse.de>