V4L/DVB (3497): Remove redundant makefile inclusion of tuner.o

VIDEO_MXB selects VIDEO_TUNER, so we don't have to include tuner.o
in the Makefile.

Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>