drm/amdgpu: fix reporting of failed msg sent to SMU (v2)

Currently send_msg_to_smc_async() only report which message
failed, but the actual failing message is the previous one,
which SMU is unable to service.

This patch reads the contents of register where the SMU is stuck
and report appropriately.

v2: fix the build (Alex)

Signed-off-by: Shirish S <shirish.s@amd.com>
Reviewed-by: Rex Zhu <Rex.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>