Revert "drm/amd/display: make dm_dp_aux_transfer return payload bytes instead of size"

This reverts commit cc195141.

This commit was problematic on other OSes. The real solution is to
leave all the error checking to DRM and don't do it in DC, which is
addressed by "Return aux replies directly to DRM" later in this patchset.

v2: Add reason for revert.

Signed-off-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>