dmaengine: usb-dmac: remove unused ‘uchan’

In usb_dmac_of_xlate(), variable ‘uchan’ is initialized but never used, which
leads to warning with W=1

drivers/dma/sh/usb-dmac.c: In function ‘usb_dmac_of_xlate’:
drivers/dma/sh/usb-dmac.c:655:24: warning: variable ‘uchan’ set but not used [-Wunused-but-set-variable]
  struct usb_dmac_chan *uchan;

So remove it.

Cc: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>