rcu: Fix dubious "if" condition in __call_rcu_nocb_enqueue()

This commit replaces an incorrect (but fortunately functional)
bitwise OR ("|") operator with the correct logical OR ("||").

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>