rcu: Fix misprint in srcu_funnel_exp_start

The srcu_funnel_exp_start() function checks to see if the srcu_struct
structure's expedited grace period counter needs updating to reflect a
newly arrived request for an expedited SRCU grace period.  Unfortunately,
the check is backwards, so this commit reverses the sense of the test.

Signed-off-by: Ildar Ismagilov <devix84@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>