arm: omap1: board-ams-delta: fix cast

Use IOMEM() macro to get rid of the following sparse warning:

arch/arm/mach-omap1/board-ams-delta.c:319:36: warning: incorrect type in initializer (different address spaces)
arch/arm/mach-omap1/board-ams-delta.c:319:36:    expected void [noderef] <asn:2>*membase
arch/arm/mach-omap1/board-ams-delta.c:319:36:    got void *<noident>

Signed-off-by: Aaro Koskinen <aaro.koskinen@nokia.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>