V4L/DVB (6787): tuner: bug-fix: default mode was set to bogus value

Fix type inconsistency in t->mode value, causing the following:

tuner' 1-0043: freq set: unknown mode: 0x0004!

(only visible with tuner debug enabled)

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