SlopController: fix formatting of logged values

While checking b/396858976 I noticed some of these log messages with
strange formatting of the values:

    InputReader: SlopController: dropping event with value .-1.000000
    InputReader: SlopController: dropping event with value .3.000000

It looks like these format strings were intended to specify the
precision after the decimal point, rather than the field width.

Bug: 245989146
Change-Id: I71691d025cc5f03b26e95f96f90ab0a2281ed43b
Test: TreeHugger
Flag: EXEMPT logs only change