uio-howto.tmpl: use unique output names

The Userspace I/O HOWTO template sets two different sections with the same
html output name (about.html).  This clearly won't work, so change the
first one to a unique "aboutthis.html" to prevent clobbering.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>
Acked-by: Hans J. Koch <hjk@linutronix.de>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>