drm/panel: st7703: Make jh057n00900_panel_desc static

This eliminates the following sparse warning:

drivers/gpu/drm/panel/panel-sitronix-st7703.c:156:26: warning: symbol
'jh057n00900_panel_desc' was not declared. Should it be static?
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Reviewed-by: Guido Günther <agx@sigxcpu.org>
[Use static const]
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200912033809.142773-1-yanaijie@huawei.com

drivers/gpu/drm/panel/panel-sitronix-st7703.c

@@ -153,7 +153,7 @@ static const struct drm_display_mode jh057n00900_mode = {
 	.height_mm   = 130,
 };
 
-struct st7703_panel_desc jh057n00900_panel_desc = {
+static const struct st7703_panel_desc jh057n00900_panel_desc = {
 	.mode = &jh057n00900_mode,
 	.lanes = 4,
 	.mode_flags = MIPI_DSI_MODE_VIDEO |