USB: xhci: Return success for vendor-specific info codes.

An xHCI host controller manufacturer can choose to implement several
vendor-specific informational completion codes.  These are all to be
treated like a successful transfer completion.

Signed-off-by: Sarah Sharp <sarah.a.sharp@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>