video: fbdev: fbmem: fix pointer reference to null device field

In function do_remove_conflicting_framebuffers, if device is NULL, there
will be null pointer reference. The patch add a check to the if expression.
Signed-off-by: Zhouyi Zhou <zhouzhouyi@gmail.com>
Acked-by: Paul Menzel <pmenzel@molgen.mpg.de>
Signed-off-by: Helge Deller <deller@gmx.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20220210065824.368355-1-zhouzhouyi@gmail.com

drivers/video/fbdev/core/fbmem.c

@@ -1579,7 +1579,7 @@ static void do_remove_conflicting_framebuffers(struct apertures_struct *a,
 			 * If it's not a platform device, at least print a warning. A
 			 * fix would add code to remove the device from the system.
 			 */
-			if (dev_is_platform(device)) {
+			if (device && dev_is_platform(device)) {
 				registered_fb[i]->forced_out = true;
 				platform_device_unregister(to_platform_device(device));
 			} else {