thermal: more gimlet PID tuning

With integral clamping working properly, previous PID terms
seem to create oscillations when tracking the set point under
load tests.  While these new PID terms don't completely resolve
that problem, they do seem to tame the variations to be less
annoying.

task/thermal/src/bsp/gimlet_bc.rs

@@ -162,12 +162,10 @@ impl Bsp {
 
             // Based on experimental tuning!
             pid_config: PidConfig {
-                // If we're > 10 degrees from the target temperature, fans
-                // should be on at full power.
                 zero: 35.0,
-                gain_p: 6.75,
-                gain_i: 0.17,
-                gain_d: 4.5,
+                gain_p: 6.1,
+                gain_i: 0.09,
+                gain_d: 2.75,
             },
 
             inputs: &INPUTS,