xhci: dbc: Don't use generic xhci inc_deq() function for dbc

xhci: dbc: Don't use generic xhci inc_deq() function for dbc

The generic inc_deq() helper takes struct xhci_hcd pointer as a parameter,
and is a lot more complex than needed for the DbC usecase.

In order to decouple xhci and DbC we have to create our own small
inc_evt_deq() helper, not relying on xhci.

Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20200723144530.9992-3-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>