usb: host: xhci: cleanup hcd private size

This patch cleanups the hcd private size to suitable size.
The previous code has "sizeof(struct xhci_hcd *)" in xhci_hc_driver
as hcd_priv_size and sizeof(struct xhci_hcd) in xhci_plat_overrides
or xhci_pci_overrides as extra_priv_size. However, the xhci driver
uses a "sizeof(struct xhcd_hcd)" memory space in each hcd
(main_hcd and shared_hcd) actually.

Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>