[media] v4l2: add const to argument of write-only s_frequency ioctl

This ioctl is defined as IOW, so pass the argument as const.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
diff --git a/drivers/media/i2c/msp3400-driver.c b/drivers/media/i2c/msp3400-driver.c
index 766305f6..77053ba 100644
--- a/drivers/media/i2c/msp3400-driver.c
+++ b/drivers/media/i2c/msp3400-driver.c
@@ -445,7 +445,7 @@
 	return 0;
 }
 
-static int msp_s_frequency(struct v4l2_subdev *sd, struct v4l2_frequency *freq)
+static int msp_s_frequency(struct v4l2_subdev *sd, const struct v4l2_frequency *freq)
 {
 	struct i2c_client *client = v4l2_get_subdevdata(sd);