drm/amd/powerplay: refine code in vega10_smumgr.c

1. return error code instand of -1.
2. print msg info if send msg failed

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