usb: typec: stusb160x: fix some signedness bugs

These variables are enums but in this situation GCC will treat them as
unsigned so the conditions are never true.

Fixes: da0cb631

 ("usb: typec: add support for STUSB160x Type-C controller family")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Link: https://lore.kernel.org/r/20201023112412.GD282278@mwanda


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