drm/amd/display: Set initial value to a divider

[why/how]
Due to compiler optimization the values would be
passed to the division function uninitialized
causing a div by zero. Initialize the numerator
and denominator to 0 and 1 to prevent division
by zero.

Signed-off-by: Mikita Lipski <mikita.lipski@amd.com>
Acked-by: Qingqing Zhuo <qingqing.zhuo@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>