xhci: Fix immediate data transfer if buffer is already DMA mapped

xhci immediate data transfer (IDT) support in 5.2-rc1 caused regression
on various Samsung Exynos boards with ASIX USB 2.0 ethernet dongle.

If the transfer buffer in the URB is already DMA mapped then IDT should
not be used. urb->transfer_dma will already contain a valid dma address,
and there is no guarantee the data in urb->transfer_buffer is valid.

The IDT support patch used urb->transfer_dma as a temporary storage,
copying data from urb->transfer_buffer into it.

Issue was solved by preventing IDT if transfer buffer is already dma
mapped, and by not using urb->transfer_dma as temporary storage.

Fixes: 33e39350 ("usb: xhci: add Immediate Data Transfer support")
Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
CC: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>