usb: musb: gadget: rxdma fix when data rcvd before usb request queued

In DMA mode, when the data is received from host before the next request
is programmed, the pio interrupt occurs and data lost since no request.

This scenario occurs sometimes in android gadget, when adb protocol receive
bigger size (>4KB) files.

The fix is not to disable the dma after completion of current rx request
so that dma interrupt will occur correctly for next request
when data received from host before next request is programmed.

Signed-off-by: Ravi Babu <ravibabu@ti.com>