arm: mach-omap1: board-h3: make nand_platdata static

Eliminates the following sparse warning:

	arch/arm/mach-omap1/board-h3.c:207:27: warning: symbol 'nand_platdata' was not declared. Should it be static?

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