drm/bridge: anx7625: Convert to use devm_kzalloc

Use devm_kzalloc instead of kzalloc and drop kfree(). Let the memory
handled by driver detach.

Signed-off-by: Hsin-Yi Wang <hsinyi@chromium.org>
Reviewed-by: Xin Ji <xji@analogixsemi.com>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220213103437.3363848-2-hsinyi@chromium.org