usb: typec: stusb160x: fix return value check in stusb160x_probe()

usb: typec: stusb160x: fix return value check in stusb160x_probe()

In case of error, the function device_get_named_child_node() returns
NULL pointer not ERR_PTR(). The IS_ERR() test in the return value check
should be replaced with NULL test.

Fixes: da0cb6310094 ("usb: typec: add support for STUSB160x Type-C controller family")
Reported-by: Hulk Robot <hulkci@huawei.com>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Reviewed-by: Amelie Delaunay <amelie.delaunay@foss.st.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Link: https://lore.kernel.org/r/20210308094839.3586773-1-weiyongjun1@huawei.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>