[media] dib8000: upd_demod_gain_period should be u32

X-Patchwork-Delegate: m.chehab@samsung.com
As shown at the code, upd_demod_gain_period is used to write
to two 16-bit registers:
    dib8000_write_word(state, 1946, upd_demod_gain_period & 0xFFFF);
    dib8000_write_word(state, 1947, reg | (1<<14) | ((upd_demod_gain_period >> 16) & 0xFF));

So, it should be declared as u32.

This fixes the following smatch warning:
	drivers/media/dvb-frontends/dib8000.c:1282 dib8000_agc_startup() warn: right shifting more than type allows

Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>