pinctrl: samsung: Validate alias coming from DT

Driver uses alias from Device Tree as an index of pin controller data
array.  In case of a wrong DTB or an out-of-tree DTB, the alias could be
outside of this data array leading to out-of-bounds access.

Depending on binary and memory layout, this could be handled properly
(showing error like "samsung-pinctrl 3860000.pinctrl: driver data not
available") or could lead to exceptions.

Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Cc: <stable@vger.kernel.org>
Fixes: 30574f0d ("pinctrl: add samsung pinctrl and gpiolib driver")
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Tomasz Figa <tomasz.figa@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>