[PATCH] m68k: fix __iounmap for 030

Ignore empty pmd entry during iomap (these are the holes between the
mappings).

Signed-off-by: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>