The conversion of acpi/enumeration.txt to RST included one markup error,
leading to many warnings like:
.../firmware-guide/acpi/enumeration.rst:430: WARNING: Unexpected indentation.
Add the missing colon and create some peace.
Fixes: c24bc66e8157 ("Documentation: ACPI: move enumeration.txt to firmware-guide/acpi and convert to reST")
Cc: Changbin Du <changbin.du@gmail.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>