spi: fix pointer-integer size mismatch warning

Fix the pointer-integer size mismatch warning below:
	drivers/spi/spi-gpio.c: In function ‘spi_gpio_setup’:
	drivers/spi/spi-gpio.c:252:8: warning: cast from pointer to integer of
			different size [-Wpointer-to-int-cast]
	   cs = (unsigned int) spi->controller_data;
	        ^

Signed-off-by: SeongJae Park <sj38.park@gmail.com>
Signed-off-by: Mark Brown <broonie@linaro.org>