USB: QTI_DPL: don't send two 0-len packets during disconnect

A 0-len packet is sent to user space upon disconnect. The current code
is sending two 0-len packets in gqti_ctrl_disconnect for DPL function.
The gqti_ctrl_disconnect() calls qti_ctrl_queue_notify() to send the
0-len packet and there is no need to queue the 0-length packet
explicitly by calling gqti_ctrl_send_cpkt_tomodem().

Change-Id: I0fe8c4f9f9003dae912a8f051ce2ffd7b3d3a65a
Signed-off-by: Pavankumar Kondeti <pkondeti@codeaurora.org>