genirq: Update DocBook comments

Fix some parts to match the actual code.

[ tglx: Resolved the FIXMEs Gerd put in ]

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Link: http://lkml.kernel.org/r/%3C1302426113-13808-3-git-send-email-geert%40linux-m68k.org%3E


Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-doc@vger.kernel.org