rcutorture: Decorate failing reader segments with last CPU ID

rcutorture: Decorate failing reader segments with last CPU ID

In kernels built with CONFIG_RCU_TORTURE_TEST_LOG_CPU=y, the CPU is
logged at the beginning of each reader segment.  This commit further
logs it at the end of the full set of reader segments in order to show
any migration that might have occurred during the last reader segment.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>