V4L/DVB (13521): dib8000: fix compile warning

Trivial fix for this bogus compile warning:

v4l/dib8000.c:958: warning: 'ncoeff' may be used uninitialized in this function

Note: ncoeff is never used uninitialized, but the compiler couldn't
figure that out.

Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>