ARM: shmobile: add new __iomem annotation for new code

While we fixed up all instances that were already present in v3.6,
this one came in through new code.

Without this patch, building kzm9g_defconfig results in:

arch/arm/mach-shmobile/board-kzm9g.c: In function 'kzm9g_restart':
arch/arm/mach-shmobile/board-kzm9g.c:781:2: warning: passing argument 2 of '__raw_writel' makes pointer from integer without a cast [enabled by default]

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>
Cc: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Cc: Tetsuyuki Kobayashi <koba@kmckk.co.jp>
Cc: Simon Horman <horms@verge.net.au>