xhci: replace real & fake port with pointer to root hub port

xhci: replace real & fake port with pointer to root hub port

Variables real & fake port do not convey their purpose, thus they are
replaced with a pointer to the root hub port 'struct xhci_port *rhub_port'.
'rhub_port' contains real & fake ports in zero-based format, which happens
to be more widely used inside the xHCI driver:
 - 'real_port' is ('rhub_port->hw_portnum' + 1)
 - 'fake_port' is ('rhub_port->hcd_portnum' + 1)

One reason for real port being one-based, is to signal other functions in
case struct 'xhci_virt_device' initialization failed, in this case the
value will remain 0. This is no longer needed, instead we check whether
or not 'rhub_port' is 'NULL'.

Signed-off-by: Niklas Neronin <niklas.neronin@intel.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20240229141438.619372-3-mathias.nyman@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>