drm/mediatek: remove cast to pointers passed to kfree

Remove unnecessary casts to pointer types passed to kfree.
Issue detected by coccinelle:
@@
type t1;
expression *e;
@@

-kfree((t1 *)e);
+kfree(e);

Signed-off-by: Wambui Karuga <wambui.karugax@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20191023111107.9972-1-wambui.karugax@gmail.com

drivers/gpu/drm/mediatek/mtk_drm_gem.c

@@ -271,7 +271,7 @@ void *mtk_drm_gem_prime_vmap(struct drm_gem_object *obj)
 			       pgprot_writecombine(PAGE_KERNEL));
 
 out:
-	kfree((void *)sgt);
+	kfree(sgt);
 
 	return mtk_gem->kvaddr;
 }
@@ -285,5 +285,5 @@ void mtk_drm_gem_prime_vunmap(struct drm_gem_object *obj, void *vaddr)
 
 	vunmap(vaddr);
 	mtk_gem->kvaddr = 0;
-	kfree((void *)mtk_gem->pages);
+	kfree(mtk_gem->pages);
 }