drm/amd/pp: Fix set wrong temperature range on smu7

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>