pinctrl: bcm: ns: Use uintptr_t for casting data

Fix up a compiler error on 64bit architectures where pointers
and integers differ in size.

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>