drm/amd/display: Align phantom pipe dst/src scaling with main for subvp

[WHY?]
Subvp src/dst stream rectangles are not being created with the same scaling
factors as the main stream.

[HOW?]
Make sure subvp stream src rectangle scales its height to have the same src/dst
ratio as the main stream.

Reviewed-by: Alvin Lee <Alvin.Lee2@amd.com>
Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Acked-by: Tom Chung <chiahsuan.chung@amd.com>
Signed-off-by: Dillon Varone <Dillon.Varone@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>