rcutorture: Use 100ms buckets for forward-progress callback histograms

This commit narrows the scope of each bucket of the forward-progress
callback-invocation histograms from one second to 100 milliseconds, which
aids debugging of forward-progress problems by making shorter-duration
callback-invocation stalls visible.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>