drm/amd/powerplay: remove smu mutex lock in smu_hw_init

the smu mutex lock is unnecessary in smu hw init.

Signed-off-by: Kevin Wang <kevin1.wang@amd.com>
Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>