lockdep: Complain only once about RCU in extended quiescent state

Currently, lockdep_rcu_suspicious() complains twice about RCU read-side
critical sections being invoked from within extended quiescent states,
for example:

	RCU used illegally from idle CPU!
	rcu_scheduler_active = 2, debug_locks = 1
	RCU used illegally from extended quiescent state!

This commit therefore saves a couple lines of code and one line of
console-log output by eliminating the first of these two complaints.

Link: https://lore.kernel.org/lkml/87wo4wnpzb.fsf@nanos.tec.linutronix.de


Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Will Deacon <will@kernel.org>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>