drm/amd/pm: suppress compile warning about possible unaligned accesses

Suppress the following compile warning:
   In file included from drivers/gpu/drm/amd/amdgpu/../pm/swsmu/smu13/smu_v13_0_0_ppt.c:39:
>> drivers/gpu/drm/amd/amdgpu/../pm/inc/smu_v13_0_0_pptable.h:194:39:
warning: field overdrive_table within 'struct smu_13_0_0_powerplay_table' is
less aligned than 'struct smu_13_0_0_overdrive_table' and is usually due to
'struct smu_13_0_0_powerplay_table' being packed,
which can lead to unaligned accesses [-Wunaligned-access]

Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Evan Quan <evan.quan@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>