spi: fix SPI_BIT_MASK so it always fits into 32-bits

On a 64-bit platform, ~0UL fills 64-bits, which causes SPI_BIT_MASK(32)
not to fit into 32 bits. This causes a warning when the result is assigned
to a 32-bit variable. Use ~0U instead to prevent this. This fixes:

drivers/spi/spi-gpio.c: In function 'spi_gpio_probe':
drivers/spi/spi-gpio.c:446:2: warning: large integer implicitly truncated to unsigned type [-Woverflow]
Reported-by: Nkbuild test robot <fengguang.wu@intel.com>
Signed-off-by: NStephen Warren <swarren@nvidia.com>
Signed-off-by: NMark Brown <broonie@linaro.org>

include/linux/spi/spi.h

@@ -309,7 +309,7 @@ struct spi_master {
 	/* bitmask of supported bits_per_word for transfers */
 	u32			bits_per_word_mask;
 #define SPI_BPW_MASK(bits) BIT((bits) - 1)
-#define SPI_BIT_MASK(bits) (((bits) == 32) ? ~0UL : (BIT(bits) - 1))
+#define SPI_BIT_MASK(bits) (((bits) == 32) ? ~0U : (BIT(bits) - 1))
 #define SPI_BPW_RANGE_MASK(min, max) (SPI_BIT_MASK(max) - SPI_BIT_MASK(min - 1))
 
 	/* other constraints relevant to this driver */