[media] radio-si476x: vidioc_s* now uses a const parameter

[media] radio-si476x: vidioc_s* now uses a const parameter

vidioc_s_tuner, vidioc_s_frequency and vidioc_s_register now
uses a constant argument. So, the driver reports warnings:

	drivers/media/radio/radio-si476x.c:1196:2: warning: initialization from incompatible pointer type [enabled by default]
	drivers/media/radio/radio-si476x.c:1196:2: warning: (near initialization for 'si4761_ioctl_ops.vidioc_s_tuner') [enabled by default]
	drivers/media/radio/radio-si476x.c:1199:2: warning: initialization from incompatible pointer type [enabled by default]
	drivers/media/radio/radio-si476x.c:1199:2: warning: (near initialization for 'si4761_ioctl_ops.vidioc_s_frequency') [enabled by default]
	drivers/media/radio/radio-si476x.c:1209:2: warning: initialization from incompatible pointer type [enabled by default]
	drivers/media/radio/radio-si476x.c:1209:2: warning: (near initialization for 'si4761_ioctl_ops.vidioc_s_register') [enabled by default]

This is due to a (soft) merge conflict, as both this driver and the
const patches were applied for the same Kernel version.

Cc: Hans Verkuil <hans.verkuil@cisco.com>
Cc: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>