Staging: rtl81*: Fix spelling fuction -> function in comments

Obviously the wrong spelling was copied a lot of times.

A similar patch for the non-staging part of linux
is committed by Jiri Kosina.

Cc: devel@driverdev.osuosl.org
Signed-off-by: Stefan Weil <weil@mail.berlios.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>