rcu/nocb: Choose the right rcuog/rcuop kthreads to output

The show_rcu_nocb_gp_state() function is supposed to dump out the rcuog
kthread and the show_rcu_nocb_state() function is supposed to dump out
the rcuo[ps] kthread.  Currently, both do a mixture, which is not optimal
for debugging, even though it does not affect functionality.

This commit therefore adjusts these two functions to focus on their
respective kthreads.

Signed-off-by: Zqiang <qiang1.zhang@intel.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>