[media] v4l2-dv-timings: print refresh rate with better precision

In many cases, refresh rate is not exact integer. In such cases,
fraction was lost and it used to print, say, 59 in case of 59.94.
Now, capturing the fraction up to 2 decimal places.

Signed-off-by: Prashant Laddha <prladdha@cisco.com>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>