docs: override section id to avoid '/' in filenames

The section id is generated from the section title and is used to create
the html output filename, which therefore causes problems if it includes
a '/' character.

Cc: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Thomas Wood <thomas.wood@intel.com>

lib/intel_mmio.c

@@ -51,6 +51,7 @@
  * @short_description: Register access and sideband I/O library
  * @title: I/O
  * @include: intel_io.h
+ * @section_id: intel-gpu-tools-IO
  *
  * This library provides register I/O helpers in both a basic version and a more
  * fancy version which also handles forcewake and can optionally check registers