drm/amd/powerplay: fix compile error with ARCH=arc

Fix the compile error below:
drivers/gpu/drm/amd/amdgpu/../powerplay/smu_v11_0.c: In function 'smu_v11_0_init_microcode':
>> arch/arc/include/asm/bug.h:22:2: error: implicit declaration of function 'pr_warn'; did you mean 'pci_warn'? [-Werror=implicit-function-declaration]
      22 |  pr_warn("BUG: failure at %s:%d/%s()!\n", __FILE__, __LINE__, __func__); \
         |  ^~~~~~~
drivers/gpu/drm/amd/amdgpu/../powerplay/smu_v11_0.c:176:3: note: in expansion of macro 'BUG'
     176 |   BUG();

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>