drm/panel: ili9322: Remove redundant volatle_reg() operation

The ili9322 driver has a volatile_reg() operation in it's regmap which
always returns false. This is redundant since it is the default in the
regmap core, remove the operation for a trivial code size and performance
improvement.

Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20231001-drm-sn65dsi83-maple-v1-1-5519799a55e5@kernel.org