drm/amd/pp: Fix NULL point check error in smu_set_watermarks_for_clocks_ranges

It is caused by
'commit d6c9a7dc86cd ("drm/amd/pp: Move common code to smu_helper.c")'

Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>