V4L/DVB (3739): Add support for FE_GET_FRONTEND to or51132 frontend

Adds the FE_GET_FRONTEND ioctl to the or51132 frontend.  Current modulation is
read from the hardware, while frequency is taken from the driver's state.

Signed-off-by: Trent Piepho <xyzzy@speakeasy.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>