drm/panel: update EDID BLOB in panel_simple_get_modes()

This stashes away the EDID data so that the sysfs per-connector file
"edid" can display it. Without this change, the "edid" file is always
empty.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>