drm/amd/display: fix backwards byte order in rx_caps.

We were using incorrect byte order after we started using the drm_defines
So fix it.

Fixes: 02837a91

 ("drm/amd/display: add and use defines from drm_hdcp.h")
Signed-off-by: JinZe.Xu <JinZe.Xu@amd.com>
Signed-off-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Reviewed-by: Wenjing Liu <Wenjing.Liu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>