USB: gadget: f_mtp: Return zero result for successful file transfer.

Returning number of bytes transfered does not work for files > 2 gig
since ioctl() result is a signed integer.

Change-Id: Id4d18fe77110d1bd390106a12f6eb1c866042a15
Signed-off-by: Mike Lockwood <lockwood@android.com>
Signed-off-by: Chandra Devireddy <cdevired@codeaurora.org>
Merge "USB: gadget: f_mtp: Return zero result for successful file transfer." into android-msm-2.6.32