es1-ap-usb: don't use 'es1' after it is freed

greybus_remove_hd() will free memory allocated to 'es1' and so using it after
the routine has returned isn't right.

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