drm/amd/display: Initialize denominators' default to 1

In the Linux kernel, the following vulnerability has been resolved:

drm/amd/display: Initialize denominators' default to 1

[WHAT & HOW]

Variables used as denominators and maybe not assigned to other values,

should not be 0. Change their default to 1 so they are never 0.

This fixes 10 DIVIDE_BY_ZERO issues reported by Coverity.