rcu: RCU-based detection of stalled CPUs for Classic RCU, fix

fix the !CONFIG_RCU_CPU_STALL_DETECTOR path:

 kernel/rcuclassic.c: In function '__rcu_pending':
 kernel/rcuclassic.c:609: error: too few arguments to function 'check_cpu_stall'

Signed-off-by: Ingo Molnar <mingo@elte.hu>