drm/amdgpu: remove duplicate return statement

Remove a redundant identical return statement, it has no use.

Detected by CoverityScan, CID#1454586 ("Structurally dead code")

Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>