monitor: Tach input to double

It was found that after the Value property on the Sensor.Value interface
was changed to be of double type, the tach input failed to get converted
correctly from double to int64 type when the property changed. Need to
set the tach input to be of double type explicitly.

Tested:
    Tach input values correctly read from dbus signal

Change-Id: I718375d5de50a88bcfaf8ff419e71f732d0b8a65
Signed-off-by: Matthew Barth <msbarth@us.ibm.com>
1 file changed