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

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.

Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Jerry Zuo <jerry.zuo@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>