core-api: remove an unexpected unident

As complained by Sphinx:
	Documentation/core-api/assoc_array.rst:13: WARNING: Enumerated list ends without a blank line; unexpected unindent.

This was already addressed, but not really fixed in 2ba90ccc.

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>