srcu: Disable interrupts directly in srcu_gp_end()

Interrupts are enabled in srcu_gp_end(), so this commit switches from
spin_lock_irqsave_rcu_node() and spin_unlock_irqrestore_rcu_node()
to spin_lock_irq_rcu_node() and spin_unlock_irq_rcu_node().

Link: https://lore.kernel.org/all/febb13ab-a4bb-48b4-8e97-7e9f7749e6da@moroto.mountain/



Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>