iomap.h misses the include guards.

[ Impact: cleanup ]
Signed-off-by: NRemis Lima Baima <remis.developer@googlemail.com>
Signed-off-by: NArnd Bergmann <arnd@arndb.de>
LKML-Reference: <200904301836.23885.arnd@arndb.de>
Signed-off-by: NIngo Molnar <mingo@elte.hu>