drm/amd/display: Return correct Error code for validate h_prime

[Why]
We are returning incorrect error code for validate h prime

[How]
Return the right Error code

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