video: fbdev: Fix potential NULL pointer dereference

There is a potential NULL pointer dereference in case
fb_create_modedb() fails and returns NULL.

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Rob Herring <robh@kernel.org>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>

drivers/video/fbdev/core/fbmon.c

@@ -978,6 +978,8 @@ void fb_edid_to_monspecs(unsigned char *edid, struct fb_monspecs *specs)
 	get_monspecs(edid, specs);
 
 	specs->modedb = fb_create_modedb(edid, &specs->modedb_len, specs);
+	if (!specs->modedb)
+		return;
 
 	/*
 	 * Workaround for buggy EDIDs that sets that the first