drm/panel: simple: Assign data from panel_dpi_probe() correctly

In the function panel_simple_probe() the pointer panel->desc is
assigned to the passed pointer desc. If function panel_dpi_probe()
is called panel->desc will be updated, but further on only desc
will be evaluated. So update the desc pointer to be able to use
the data from the function panel_dpi_probe().

Fixes: 4a1d0dbc ("drm/panel: simple: add panel-dpi support")

Signed-off-by: Christoph Niedermaier <cniedermaier@dh-electronics.com>
Cc: Marek Vasut <marex@denx.de>
Cc: Thierry Reding <thierry.reding@gmail.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
To: dri-devel@lists.freedesktop.org
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Marek Vasut <marex@denx.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20220201110153.3479-1-cniedermaier@dh-electronics.com