drm/amd/powerplay: a quick fix for the deadlock issue below

drm/amd/powerplay: a quick fix for the deadlock issue below

NFO: task ocltst:2028 blocked for more than 120 seconds.
     Tainted: G           OE     5.0.0-37-generic #40~18.04.1-Ubuntu
echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
cltst          D    0  2028   2026 0x00000000
all Trace:
__schedule+0x2c0/0x870
schedule+0x2c/0x70
schedule_preempt_disabled+0xe/0x10
__mutex_lock.isra.9+0x26d/0x4e0
__mutex_lock_slowpath+0x13/0x20
? __mutex_lock_slowpath+0x13/0x20
mutex_lock+0x2f/0x40
amdgpu_dpm_set_powergating_by_smu+0x64/0xe0 [amdgpu]
gfx_v8_0_enable_gfx_static_mg_power_gating+0x3c/0x70 [amdgpu]
gfx_v8_0_set_powergating_state+0x66/0x260 [amdgpu]
amdgpu_device_ip_set_powergating_state+0x62/0xb0 [amdgpu]
pp_dpm_force_performance_level+0xe7/0x100 [amdgpu]
amdgpu_set_dpm_forced_performance_level+0x129/0x330 [amdgpu]

Fixes: a64c9e15e624 ("drm/amd/powerplay: cleanup the interfaces for powergate setting through SMU")
Signed-off-by: Evan Quan <evan.quan@amd.com>
Reported-by: Rui Teng <Rui.Teng@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>