drm: Correct DP DSC macro typo

In the file drm_dp_helper.h we have a macro named
DP_DSC_THROUGHPUT_MODE_{0,1}_UPSUPPORTED, the correct name should be
DP_DSC_THROUGHPUT_MODE_{0,1}_UNSUPPORTED. This commits adjusts this typo
in the header file and in other places that attempt to access this
macro.

Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200429184142.1867987-1-Rodrigo.Siqueira@amd.com