[PATCH] USB: EHCI on non-Au1200 build fix

Including ehci-au1xxx.c on a non-Au1200 Alchemy only to have it throw
an error is stupid.

From: Ralf Baechle <ralf@linux-mips.org>
Acked-by: David Brownell <david-b@pacbell.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>