Fix the issue thermal irq was always triggered
as GPU under temperature range detected

The low temp in default thermal policy
was set to -273. so need to use int type for the low temp.
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Rex Zhu <Rex.Zhu@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>