pinctrl: at91: Fix possible out-of-boundary access

pinctrl: at91: Fix possible out-of-boundary access

at91_gpio_probe() doesn't check that given OF alias is not available or
something went wrong when trying to get it. This might have consequences
when accessing gpio_chips array with that value as an index. Note, that
BUG() can be compiled out and hence won't actually perform the required
checks.

Fixes: 6732ae5cb47c ("ARM: at91: add pinctrl support")
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Closes: https://lore.kernel.org/r/202505052343.UHF1Zo93-lkp@intel.com/
Link: https://lore.kernel.org/20250508200807.1384558-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>