V4L: ivtv: Add missing sg_init_table()

upstream commit: 165e1213

If a dma transfer is attempted for either yuv or framebuffer output, a
missing sg_init_table() call causes a kernel BUG in scatterlist.h if
CONFIG_DEBUG_SG is set.

Signed-off-by: Ian Armstrong <ian@iarmst.demon.co.uk>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@infradead.org>
Signed-off-by: Michael Krufky <mkrufky@linuxtv.org>
Signed-off-by: Chris Wright <chrisw@sous-sol.org>