usb: wusbcore: do device lookup while holding the hc mutex

This patch modifies the device notification handler to not look up the
wusb_dev object before it calls the lower-level handler routines since
the wusbhc mutex is not held when calling those routines and the device
could go away in the meantime.  Instead, let the individual notification
handlers get the device ptr if they need to after they have taken the
mutex.

Signed-off-by: Thomas Pugliese <thomas.pugliese@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>