drm/panel: Remove duplicate header

Remove duplicate header which is included twice.

Signed-off-by: Souptick Joarder <jrdr.linux@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1555183750-11028-1-git-send-email-jrdr.linux@gmail.com