drm/amd/display: fix v tap calculation for non-adaptive scaling in SPL

[Why & How]
v and h tap calculations slightly different
Use h tap calculation for both v and h tap

Reviewed-by: Navid Assadian <navid.assadian@amd.com>
Signed-off-by: Samson Tam <Samson.Tam@amd.com>
Signed-off-by: Fangzhi Zuo <jerry.zuo@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>