USB: gadget: f_mtp: Make sure request is dequeued if transfer is canceled

If the host cancels a file transfer while we have a read request pending,
call usb_ep_dequeue to cancel the read.
Also return -ECANCELED from mtp_ioctl if we are canceled in MTP_RECEIVE_FILE

CRs-Fixed: 304857
Change-Id: I8e7e622f1d0797bcdbd4bda71399879c90aaf723
Signed-off-by: Mike Lockwood <lockwood@android.com>
Signed-off-by: Chandra Devireddy <cdevired@codeaurora.org>
Merge "USB: gadget: f_mtp: Make sure request is dequeued if transfer is canceled" into android-msm-2.6.32