V4L/DVB: v4l: mem2mem_testdev: fix g_fmt NULL pointer dereference

Calling g_fmt before s_fmt resulted in a NULL pointer dereference as no
default formats were being selected on probe.
Reported-by: NNémeth Márton <nm127@freemail.hu>
Signed-off-by: NPawel Osciak <p.osciak@samsung.com>
Signed-off-by: NKyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: NMauro Carvalho Chehab <mchehab@redhat.com>

drivers/media/video/mem2mem_testdev.c

@@ -988,6 +988,9 @@ static int m2mtest_probe(struct platform_device *pdev)
 		goto err_m2m;
 	}
 
+	q_data[V4L2_M2M_SRC].fmt = &formats[0];
+	q_data[V4L2_M2M_DST].fmt = &formats[0];
+
 	return 0;
 
 err_m2m: