greybus: es2: move ap_disconnect() below ap_probe()

This makes it more readable, as the functions are present in this order
in the structure as well. Also keeping these two makes more sense.

Tested by removing the gb-es2.ko module on both EVT1.5 and qemu with
gbsim.

Signed-off-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>