libkvazaar: Set frame rate as a rational number

Updates libkvazaar to pass the exact frame rate to Kvazaar by setting
the numerator and denominator separately instead of a single floating
point number. The exact frame rate is needed for writing timing info to
the bitstream.

Requires Kvazaar version 0.8.1.

Signed-off-by: Arttu Ylä-Outinen <arttu.yla-outinen@tut.fi>
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>