docs: security: trusted-encrypted.rst: fix code-block tag

The code-block tag is at the wrong place, causing those
warnings:

    Documentation/security/keys/trusted-encrypted.rst:112: WARNING: Literal block expected; none found.
    Documentation/security/keys/trusted-encrypted.rst:121: WARNING: Unexpected indentation.
    Documentation/security/keys/trusted-encrypted.rst:122: WARNING: Block quote ends without a blank line; unexpected unindent.
    Documentation/security/keys/trusted-encrypted.rst:123: WARNING: Block quote ends without a blank line; unexpected unindent.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
Acked-by: James Morris <jamorris@linux.microsoft.com>
Acked-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>