usb: mtk-xhci: Do not explicitly set the DMA mask

usb: mtk-xhci: Do not explicitly set the DMA mask

The mtk-xhci platform glue sets the DMA mask to 32 bits on its own,
which was needed before commit fda182d80a0b ("usb: xhci: configure
32-bit DMA if the controller does not support 64-bit DMA"), but now it
has no effect, because xhci_gen_setup() sets it up for us according to
hardware capabilities. Remove the useless code.

Signed-off-by: Tomasz Figa <tfiga@chromium.org>
Link: https://lore.kernel.org/r/20191219093954.163417-1-tfiga@chromium.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>