drm/amdgpu: make smu_v13_0_7_check_fw_status() static

It's not used outside of the this file.

Reviewed-by: Kenneth Feng <kenneth.feng@amd.com>
Reviewed-by: Guchun Chen <guchun.chen@amd.com>
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>