gpio-pch: cleanup __iomem annotation usage

The __iomem annotation is to be used together with pointers used
as iowrite32() parameter. For more details see [1] and [2].

This patch will remove the following sparse warnings ("make C=1"):
 * warning: incorrect type in assignment (different address spaces)
 * warning: incorrect type in argument 1 (different address spaces)
 * warning: incorrect type in argument 2 (different address spaces)

References:
[1] A new I/O memory access mechanism (Sep 15, 2004)
    http://lwn.net/Articles/102232/

[2] Being more anal about iospace accesses (Sep 15, 2004)
    http://lwn.net/Articles/102240/Signed-off-by: Márton Németh <nm127@freemail.hu>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

drivers/gpio/gpio-pch.c

@@ -231,7 +231,7 @@ static void pch_gpio_setup(struct pch_gpio *chip)
 static int pch_irq_type(struct irq_data *d, unsigned int type)
 {
 	u32 im;
-	u32 *im_reg;
+	u32 __iomem *im_reg;
 	u32 ien;
 	u32 im_pos;
 	int ch;