drm/amd/display: Initialize denominator defaults to 1

In the Linux kernel, the following vulnerability has been resolved: drm/amd/display: Initialize denominator defaults to 1 [WHAT & HOW] Variables, used as denominators and maybe not assigned to other values, should be initialized to non-zero to avoid DIVIDE_BY_ZERO, as reported by Coverity. (cherry picked from commit e2c4c6c10542ccfe4a0830bb6c9fd5b177b7bbb7)