USB: gadget: mtp: Fix hang in ioctl(MTP_RECEIVE_FILE) for WritePartialObject

In receive_file_work, we now queue reads with length rounded up to
max packet size rather than mtp_rx_req_len.
Otherwise the read request will never complete.

Signed-off-by: Mike Lockwood <lockwood@google.com>
Signed-off-by: franciscofranco <franciscofranco.1990@gmail.com>