musb-new, dfu: first send request answer then call completions

musb-new, dfu: first send request answer then call completions

comment in ep0_txstate() states:

"report completions as soon as the fifo's loaded; there's no win
 in waiting till this last packet gets acked".

This is wrong for using dfu. In the dfu usecase we must send
a PollTimeout to the host, so the host can wait until the
U-Boot Code is ready for answering new usb requests. So the
answer which contains the PollTimeout must send *before*
U-Boot calls req->complete.

The req->complete is used in the dfu case for flushing the
medium, when entering DFU_STATE_dfuMANIFEST_SYNC state.

Change-Id: Ib2941119c72761e48e15fedbdad1ecce07ae0b3d
Signed-off-by: Heiko Schocher <hs@denx.de>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Marek Vasut <marex@denx.de>
Cc: Pantelis Antoniou <panto@antoniou-consulting.com>
Acked-by: Marek Vasut <marex@denx.de>
Acked-by: Lukasz Majewski <l.majewski@samsung.com>