drm/amd/display: Fixed bandwidth calculation error when converting fractions

[Problem]
VSR greyed out

[Root cause]
When converting fractions, we were using the integer function, which let to
a large display clock and the view was not supported

[Solution]
Change the integer to fraction functions

Signed-off-by: Logatharshan Thothiralingam <logatharshan.thothiralingam@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>