usb: dwc3: omap: get rid of dma_status

dma_status bit flag is set but never really used
so get rid of it.

Reported-by: Felipe Balbi <balbi@kernel.org>
Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>