rcutorture: Don't cpuhp_remove_state() if cpuhp_setup_state() failed

rcutorture: Don't cpuhp_remove_state() if cpuhp_setup_state() failed

[ Upstream commit fd13fe16db0d82612b260640f4e26f6d9d1e11fd ]

Currently, in CONFIG_RCU_BOOST kernels, if the rcu_torture_init()
function's call to cpuhp_setup_state() fails, rcu_torture_cleanup()
gamely passes nonsense to cpuhp_remove_state().  This results in
strange and misleading splats.  This commit therefore ensures that if
the rcu_torture_init() function's call to cpuhp_setup_state() fails,
rcu_torture_cleanup() avoids invoking cpuhp_remove_state().

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>