MAINTAINERS: Add myself as a reviewer for panel-edp.c

panel-edp changes go through the drm-misc tree (as per the "DRM PANEL
DRIVERS" entry in MAINTAINERS), but ever since splitting panel-edp out
of panel-simple I've been trying to keep a close eye on it. Make that
official by listing me as a reviewer.

Signed-off-by: Douglas Anderson <dianders@chromium.org>
Acked-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220822105340.1.I66a9a5577f9b0af66492ef13c47bc78ed85e5d6b@changeid