GMINL-3234: Tweak magneto filter window size

GMINL-3234: Tweak magneto filter window size

100 events is way too much, and besides, this value is being reduced
to one second worth of data samples anyway. That should reduce CPU
load and latency a little bit on fast magnetometers. On the ECS
Cruise 7 it shouldn't change much as the BMC150 operates at 30 Hz max.

Change-Id: I078d071dd7c5fb0b06e0fd01739679cff0ac8bef
Tracked-On: https://jira01.devtools.intel.com/browse/GMINL-3234
Signed-off-by: Patrick Porlan <patrick.porlan@intel.com>