usbip: vhci_hcd: fix NULL deref in status_show_vhci

In the Linux kernel, the following vulnerability has been resolved: usbip: vhci_hcd: fix NULL deref in status_show_vhci platform_get_drvdata() can return NULL if a VHCI host controller's probe failed (e.g. due to USB bus number exhaustion). status_show_vhci() checked for a NULL pdev but not for a NULL hcd returned by platform_get_drvdata(). Passing NULL to hcd_to_vhci_hcd() does not return NULL - it returns a pointer offset of 0x260, causing a NULL pointer dereference when that value is subsequently dereferenced. Add a NULL check on hcd before calling hcd_to_vhci_hcd(). Move status_show_not_ready() above status_show_vhci() to make it callable from the new error path without a forward declaration.