drm/amd/display: Fix swapped dimension calculations

[Why]
The values calculated in optc1_get_otg_active_size are assigned to the
wrong output parameters, vertical blank is being used for horizontal size
and vice versa. This results in DPG test pattern looking wrong during
hardware init, as the DPG dimensions get assigned from this output, and
potentially other issues.

Reviewed-by: Aric Cyr <aric.cyr@amd.com>
Acked-by: Zaeem Mohamed <zaeem.mohamed@amd.com>
Signed-off-by: Joshua Aberback <joshua.aberback@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>