spi/pxa2xx: fix warnings when compiling a 64-bit kernel

Fix following warnings seen when compiling 64-bit:

drivers/spi/spi-pxa2xx.c: In function ‘map_dma_buffers’: drivers/spi/spi-pxa2xx.c:384:7: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
drivers/spi/spi-pxa2xx.c:384:40: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
drivers/spi/spi-pxa2xx.c: In function ‘pxa2xx_spi_probe’:
drivers/spi/spi-pxa2xx.c:1572:34: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
drivers/spi/spi-pxa2xx.c:1572:34: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
drivers/spi/spi-pxa2xx.c:1572:34: warning: cast from pointer to integer of different size [-Wpointer-to-int-cast]
drivers/spi/spi-pxa2xx.c:1572:27: warning: cast to pointer from integer of different size [-Wint-to-pointer-cast]

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>