pinctrl: at91-pio4: check return value of devm_kasprintf()

devm_kasprintf() returns a pointer to dynamically allocated memory.
Pointer could be NULL in case allocation fails. Check pointer validity.
Identified with coccinelle (kmerr.cocci script).

Fixes: 77618084 ("pinctrl: introduce driver for Atmel PIO4 controller")
Depends-on: 1c4e5c47 ("pinctrl: at91: use devm_kasprintf() to avoid potential leaks")
Depends-on: 5a8f9cf2 ("pinctrl: at91-pio4: use proper format specifier for unsigned int")
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20230615105333.585304-4-claudiu.beznea@microchip.com


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>