usb: dwc3: Do not set dma coherent mask

The dma mask is correctly set up by the DT probe function, no
need to override it any more.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Sriram Dash <sriram.dash@nxp.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>