USB: UDC: net2272: Fix memory leaks

Like net2280 (on which it was based), the net2272 UDC driver has a
problem with leaking memory along some of its failure pathways.  It
also has another problem, not previously noted, in that some of the
failure pathways will call usb_del_gadget_udc() without first calling
usb_add_gadget_udc_release().  And it leaks memory by calling kfree()
when it should call put_device().

Until now it has been impossible to handle the memory leaks, because of
lack of support in the UDC core for separately initializing and adding
gadgets, or for separately deleting and freeing gadgets.  An earlier
patch in this series adds the necessary support, making it possible to
fix the outstanding problems properly.

This patch adds an "added" flag to the net2272 structure to indicate
whether or not the gadget has been registered (and thus whether or not
to call usb_del_gadget()), and it fixes the deallocation issues by
calling usb_put_gadget() at the appropriate places.

A similar memory leak issue, apparently never before recognized, stems
from the fact that the driver never initializes the drvdata field in
the gadget's embedded struct device!  Evidently this wasn't noticed
because the pointer is only ever used as an argument to kfree(), which
doesn't mind getting called with a NULL pointer. In fact, the drvdata
for gadget device will be written by usb_composite_dev structure if
any gadget class is loaded, so it needs to use usb_gadget structure
to get net2280 private data.

CC: Anton Vasilyev <vasilyev@ispras.ru>
CC: Evgeny Novikov <novikov@ispras.ru>
CC: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Reviewed-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Peter Chen <peter.chen@nxp.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>