lib: utils/gpio: Fix RV32 compile error for designware GPIO driver

Currently, we see following compile error in the designeware GPIO driver
for RV32 systems:

lib/utils/gpio/fdt_gpio_designware.c:115:20: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
  115 |         chip->dr = (void *)addr + (bank * 0xc);
      |                    ^
lib/utils/gpio/fdt_gpio_designware.c:116:21: error: cast to pointer from integer of different size [-Werror=int-to-pointer-cast]
  116 |         chip->ext = (void *)addr + (bank * 4) + 0x50;

We fix the above error using an explicit type-cast to 'unsigned long'.

Fixes: 7828eeba ("gpio/desginware: add Synopsys DesignWare APB GPIO support")
Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Xiang W <wxjstz@126.com>