rcu: Fix blimit type for trace_rcu_batch_start()

When the type of global variable blimit changed from int to long, the
type of the blimit argument of trace_rcu_batch_start() needed to have
changed.  This commit fixes this issue.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>