drm: panel: simple: specify bpc for powertip_ph800480t013_idf02

Specify bpc value for the powertip_ph800480t013_idf02 panel to stop drm
code from complaining about unexpected bpc value (0).

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.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/20230727172445.1548834-1-dmitry.baryshkov@linaro.org