drm/amd/display: Set VSC SDP Colorimetry same way for MST and SST

The previous check for the is_vsc_sdp_colorimetry_supported flag
for MST sink signals did nothing. Simplify the code and use the
same check for MST and SST.

Cc: stable@vger.kernel.org
Reviewed-by: Agustin Gutierrez <agustin.gutierrez@amd.com>
Acked-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>