srcu: Release early_srcu resources when no longer in use

Kernels built with the CONFIG_TREE_SRCU Kconfig option set and then
booted with rcupdate.rcu_self_test=1 and srcutree.convert_to_big=1 will
test Tree SRCU during early boot.  The early_srcu structure's srcu_node
array will be allocated when init_srcu_struct_fields() is invoked,
but after the test completes this early_srcu structure will not be used.

This commit therefore invokes cleanup_srcu_struct() to free that srcu_node
structure.

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