[PATCH] iomem annotations (ac3200.c)

no need to mess with (wrong) casts for ->mem_start, when we have the
original iomem pointer used to set ->mem_start in the first place...

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>