USB: EHCI: remove bogus #error

The EHCI host controller driver can be built standalone now,
without enabling any of the available bus glue drivers, so
there is not really a reason to error out here:

drivers/usb/host/ehci-hcd.c:1303:2: error:
 #error "missing bus glue for ehci-hcd"  #error "missing bus glue for ehci-hcd"

The alternative would be to change the Kconfig code to build
the ehci-hcd module only if any of the symbols below are
in fact enabled.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>