USB: gadget: f_mtp: Zero length packet fixes

Send zero length packets at end of transfers that are a multiple of the
bulk max packet size as required by MTP.

Change-Id: I46cd853791bc8c0079a085367068009435343a0d
Signed-off-by: Mike Lockwood <lockwood@android.com>
Signed-off-by: Chandra Devireddy <cdevired@codeaurora.org>
Merge "USB: gadget: f_mtp: Zero length packet fixes" into android-msm-2.6.32