pinctrl: pinconf-generic: Validate fwnode instead of device node

pinctrl: pinconf-generic: Validate fwnode instead of device node

Currently we convert device node to fwnode in the
pinconf_generic_parse_dt_config() and then validate the device node.
This is confusing order. Instead, assign fwnode and validate it.

Fixes: e002d162654b ("pinctrl: pinconf-generic: Use only fwnode API in parse_dt_cfg()")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Linus Walleij <linusw@kernel.org>