Back off chassis fan proportional constant

Ambient temperature swings should be slow enough, with a slow enough thermal response
from the PCB, to make primary control via integrator viable.  This slows down the fan
responses and prevents audible "hunting" as the ambient sensor changes value more
rapidly than the chassis fans actually need to react.

meta-openbmc-machines/meta-openpower/meta-rcs/meta-talos/recipes-phosphor/fans/phosphor-fan-control-events-config-native/events.yaml

@@ -739,7 +739,7 @@ events:
                           value: 1
                           type: int64_t
                       kp:
-                          value: 500
+                          value: 50
                           type: int64_t
                       ki:
                           value: 25