drm/amd/pm: Fix a bug in semaphore double-lock

Fix a bug in smu_cmn_send_msg_without_waiting() in
that this function does not need to take the
smu->message_lock mutex in order to send a message
down to the SMU. The mutex is acquired by the
caller of this function instead.

Cc: Alex Deucher <Alexander.Deucher@amd.com>
Cc: Changfeng Zhu <Changfeng.Zhu@amd.com>
Cc: Huang Rui <ray.huang@amd.com>
Fixes: 5810323b ("drm/amd/pm: Fix a bug communicating with the SMU (v5)")
Signed-off-by: Luben Tuikov <luben.tuikov@amd.com>
Reviewed-by: Alex Deucher <Alexander.Deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>