[SPARC]: sunzilog warning fixes

From: William Lee Irwin III <wli@holomorphy.com>

This small patch silences some iomem-related warnings in sunzilog.c by
declaring mapped_addr as void __iomem * and inserting a cast in one case.

Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>