usb: dwc3: dwc3-omap: Do not read DMA status

usb: dwc3: dwc3-omap: Do not read DMA status

Commit af566a0be6e49 ("usb: dwc3: omap: get rid of dma_status") rendered
reading DMA status from the H/W even more redundant.  The variable hasn't
been read/used since 2016.  Remove the set but unused variable and the call
which populates it.

Fixes the following W=1 warning:

 drivers/usb/dwc3/dwc3-omap.c: In function ‘dwc3_omap_probe’:
 drivers/usb/dwc3/dwc3-omap.c:460:8: warning: variable ‘reg’ set but not used [-Wunused-but-set-variable]
 460 | u32 reg;
 | ^~~

Cc: Felipe Balbi <balbi@kernel.org>
Cc: Andrzej Siewior <bigeasy@linutronix.de>
Cc: linux-omap@vger.kernel.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20200702144625.2533530-9-lee.jones@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>