USB: ehci-platform: remove update_device

The update_device callback is not needed and the function used here is
from the pci ehci driver. Without this patch we get a compile error if
ehci-platform is compiled without ehci-pci.

Signed-off-by: Hauke Mehrtens <hauke@hauke-m.de>
Cc: stable <stable@vger.kernel.org> [3.4]
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>