Although the mag modules in the daemon were limited to 20hz, the HAL
was announcing 50hz. Fix the HAL value so that it matches the daemon
implementation
android.hardware.cts.SingleSensorTests#testMagneticFieldUncalibrated_100hz,
testMagneticFieldUncalibrated_100hz, testMagneticFieldUncalibrated_25hz,
testMagneticFieldUncalibrated_50hz, testMagneticFieldUncalibrated_fastest,
testMagneticField_100hz, testMagneticField_200hz, testMagneticField_25hz,
testMagneticField_fastest
Ref CRACKLING-962
Change-Id: Ia74473d72b2275a3f86e3ff4735b89fd89ddd294