drm/amdgpu/sdma5: incorrect variable type for gpu address

Incorrect programming with 64bit gpu address assignment for
32bit variable.

Signed-off-by: Jack Xiao <Jack.Xiao@amd.com>
Reviewed-by: Xiaojie Yuan <xiaojie.yuan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>