omap: get rid of a useless cast

That cast was annyoing for quite a while. Now
omap_ctrl_base_get() returns void __iomem *
and __raw_read/write friends uses void __iomem *
so there's no need for casting.

Signed-off-by: Felipe Balbi <felipe.balbi@nokia.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>