drm/panel: panasonic-vvx10f034n00: More return value fixes

A couple more return value fixes which Philippe brought up during our
previous review.

Suggested-by: Philippe CORNU <philippe.cornu@st.com>
Reviewed-by: Philippe Cornu <philippe.cornu@st.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20180117213751.54668-1-seanpaul@chromium.org