docs: translations: zh_CN: memory-hotplug.rst: fix a typo

memory_hotplug.rst -> memory-hotplug.rst

Fixes: 62012754 ("docs/zh_CN: add core api memory_hotplug translation")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/b22b772c23f531708a9bc025d56c0312a53bd6c9.1634630486.git.mchehab+huawei@kernel.org


Signed-off-by: Jonathan Corbet <corbet@lwn.net>