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>