usb: gadget: f_hid: fix: Prevent accessing released memory

commit aa65d11aa008f4de58a9cee7e121666d9d68505e upstream.

When we unlock our spinlock to copy data to user we may get
disabled by USB host and free the whole list of completed out
requests including the one from which we are copying the data
to user memory.

To prevent from this let's remove our working element from
the list and place it back only if there is sth left when we
finish with it.

Fixes: 99c51500 ("usb: gadget: hidg: register OUT INT endpoint for SET_REPORT")
Tested-by: David Lechner <david@lechnology.com>
Signed-off-by: Krzysztof Opasiak <k.opasiak@samsung.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>