docs: kvm: api.rst: add missing spaces

docs: kvm: api.rst: add missing spaces

There are some warnings:

   Documentation/virt/kvm/api.rst:4354: WARNING: Definition list ends without a blank line; unexpected unindent.
   Documentation/virt/kvm/api.rst:4358: WARNING: Definition list ends without a blank line; unexpected unindent.
   Documentation/virt/kvm/api.rst:4363: WARNING: Definition list ends without a blank line; unexpected unindent.

Produced by the lack of identation on a single line. That
caused the literal block to end prematurely.

Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/b6b3679b6c2329dc9b16d397c289b5ade0184c63.1599660067.git.mchehab+huawei@kernel.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>