swsmu/amdgpu_smu: Fix the wrong if-condition

The logical operator '&&' will make
smu->ppt_funcs->set_gfx_power_up_by_imu segment fault when
smu->ppt_funcs is NULL.

Signed-off-by: Yu Songping <yusongping@huawei.com>
Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>