spi/imx: mark base member in spi_imx_data as __iomem

This fixes 36 sparse warnings like:

	drivers/spi/spi-imx.c:143:1: warning: incorrect type in argument 1 (different address spaces)
	drivers/spi/spi-imx.c:143:1:    expected void const volatile [noderef] <asn:2>*<noident>
	drivers/spi/spi-imx.c:143:1:    got void *
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

drivers/spi/spi-imx.c

@@ -83,7 +83,7 @@ struct spi_imx_data {
 	struct spi_bitbang bitbang;
 
 	struct completion xfer_done;
-	void *base;
+	void __iomem *base;
 	int irq;
 	struct clk *clk;
 	unsigned long spi_clk;