drm/panel: synaptics-r63353: Fix regulator unbalance

drm/panel: synaptics-r63353: Fix regulator unbalance

The shutdown function can be called when the display is already
unprepared. For example during reboot this trigger a kernel
backlog. Calling the drm_panel_unprepare, allow us to avoid
to trigger the kernel warning.

Fixes: 2e87bad7cd33 ("drm/panel: Add Synaptics R63353 panel driver")
Tested-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Signed-off-by: Michael Trimarchi <michael@amarulasolutions.com>
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Reviewed-by: Neil Armstrong <neil.armstrong@linaro.org>
Reviewed-by: Jessica Zhang <quic_jesszhan@quicinc.com>
Link: https://lore.kernel.org/r/20241205163002.1804784-1-dario.binacchi@amarulasolutions.com
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20241205163002.1804784-1-dario.binacchi@amarulasolutions.com