drm/amd/amdgpu: Improve amdgpu_dpm* macros to avoid unexpected result (v2)

The two macros returns are values which probably are used
in the expression of calculation. Without the brackets
the result of the expression may be wrong.

v2: agd: squash both patches together

Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Eric Huang <JinHuiEric.Huang@amd.com>