MAINTAINERS: update xgifb maintainer's e-mail address

All patches sent to the maintainer address bounce:

   Diagnostic-Code: smtp; 550 5.1.1 <apatard@mandriva.com>: Recipient address
       rejected: User unknown in virtual mailbox table

The address found in drivers/staging/xgifb/TODO seems to work better.

Signed-off-by: Aaro Koskinen <aaro.koskinen@iki.fi>
Cc: arnaud.patard@rtp-net.org
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>