soc/rockchip/rk3399/display.c: Remove unuseful 'return' in void function

Change-Id: I8b5537bb6d0cb934aadb0eba8ba4f51dd53026c2
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/61488
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin Roth <martinroth@google.com>

src/soc/rockchip/rk3399/display.c

@@ -162,6 +162,4 @@ retry_edp:
 	}
 	mainboard_power_on_backlight();
 	fb_new_framebuffer_info_from_edid(&edid, (uintptr_t)0);
-
-	return;
 }