[media] lgdt3306a: one bit fields should be unsigned

Fix two smatch warnings:
	drivers/media/dvb-frontends/lgdt3306a.h:53:28: error: dubious one-bit signed bitfield
	drivers/media/dvb-frontends/lgdt3306a.h:56:33: error: dubious one-bit signed bitfield

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