drm/msm/a6xx: Fix out of bound IO access in a6xx_get_gmu_registers

drm/msm/a6xx: Fix out of bound IO access in a6xx_get_gmu_registers

REG_A6XX_GMU_AO_AHB_FENCE_CTRL register falls under GMU's register
range. So, use gmu_write() routines to write to this register.

Fixes: 1707add81551 ("drm/msm/a6xx: Add a6xx gpu state")
Cc: stable@vger.kernel.org
Signed-off-by: Akhil P Oommen <akhilpo@oss.qualcomm.com>
Reviewed-by: Konrad Dybcio <konrad.dybcio@oss.qualcomm.com>
Patchwork: https://patchwork.freedesktop.org/patch/688993/
Message-ID: <20251118-kaana-gpu-support-v4-1-86eeb8e93fb6@oss.qualcomm.com>
Signed-off-by: Rob Clark <robin.clark@oss.qualcomm.com>