drm/amdgpu: remove redundant variable r and redundant return statement

There is a return statement that is not reachable and a variable that
is not used.  Remove them.

Addresses-Coverity: ("Structurally dead code")
Fixes: de7b45ba ("drm/amdgpu: cleanup creating BOs at fixed location (v2)")
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>