xhci: dbc: Add device pointer to dbc structure

xhci: dbc: Add device pointer to dbc structure

Currently the dbc structure contains a pointer to struct xhci_hcd,
and dbc functions use that to dig up the underlying device pointer.

We are trying to decouple xhci and dbc code, and prepare for
code that use dbc such as dbctty into into real device drivers.
This is one step along the way.

Keep functionality the same and keep the xhci pointer, and
let the new device pointer point to the xhci device for now.

Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20200723144530.9992-8-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>