staging: slicoss: fix different address space warnings

Remove incorrect __iomem annotation.

This patch fix the following sparse warnings in slicoss driver:
warning: incorrect type in assignment (different address spaces)

Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>