xenfb: Fix graphic_console_init() build failure

xenfb: Fix graphic_console_init() build failure

In commit 5643706a095044d75df1c0588aac553a595b972b (console: add head
to index to qemu consoles.) graphic_console_init() was extended to take
an additional argument, but xenfb was not updated accordingly. Fix it.

Cc: Gerd Hoffmann <[email protected]>
Signed-off-by: Andreas Färber <[email protected]>
Reviewed-by: Stefan Weil <[email protected]>
Reviewed-by: Don Slutz <[email protected]>
Signed-off-by: Peter Maydell <[email protected]>
Message-id: 1394228528[email protected]