In the .s_frame_interval() subdev op, don't accept or set a
frame interval with a zero numerator or denominator. This fixes
a v4l2-compliance failure:

fail: v4l2-test-formats.cpp(1146):
cap->timeperframe.numerator == 0 || cap->timeperframe.denominator == 0
test VIDIOC_G/S_PARM: FAIL
Signed-off-by: Steve Longerbeam <slongerbeam@gmail.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>