drm/amd/display: Fix subvp+drr logic errors

[Why]
There is some logic error where the wrong variable was used to check for
OTG_MASTER and DPP_PIPE.

[How]
Add booleans to confirm that the expected pipes were found before
validating schedulability.

Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Acked-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Reviewed-by: Samson Tam <samson.tam@amd.com>
Reviewed-by: Chaitanya Dhere <chaitanya.dhere@amd.com>
Signed-off-by: Alvin Lee <alvin.lee2@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>