media: em28xx: fix PCTV 290e LNA oops

commit 3ec40dcfb413214b2874aec858870502b61c2202 upstream.

Pointer to device state has been moved to different location during
some change. PCTV 290e LNA function still uses old pointer, carried
over FE priv, and it crash.

Reported-by: Janne Kujanpää <jikuja@iki.fi>
Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>