xhci: check control context is valid before dereferencing it.

Don't dereference ctrl_ctx before checking it's valid.
Issue reported by Klockwork

Signed-off-by: Mathias Nyman <mathias.nyman@linux.intel.com>
Link: https://lore.kernel.org/r/20210406070208.3406266-3-mathias.nyman@linux.intel.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>