USB: musb: da8xx: remove clock con_id

There is only one clock for the DA8xx MUSB device, so we don't need the
con_id, so remove it. This way we don't have to add an unnecessary
property to the device tree bindings for the clock.

Signed-off-by: David Lechner <david@lechnology.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>