[media] mem2mem_testdev: Remove casting the return value which is a void pointer

Casting the return value which is a void pointer is redundant.
The conversion from void pointer to any other pointer type is
guaranteed by the C programming language.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Kamil Debski <k.debski@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>

drivers/media/platform/mem2mem_testdev.c

@@ -1090,8 +1090,7 @@ unreg_dev:
 
 static int m2mtest_remove(struct platform_device *pdev)
 {
-	struct m2mtest_dev *dev =
-		(struct m2mtest_dev *)platform_get_drvdata(pdev);
+	struct m2mtest_dev *dev = platform_get_drvdata(pdev);
 
 	v4l2_info(&dev->v4l2_dev, "Removing " MEM2MEM_TEST_MODULE_NAME);
 	v4l2_m2m_release(dev->m2m_dev);