ARM: mv78xx0: fix win_cfg_base prototype

Patch b6d1c33a "ARM: Orion: Consolidate the address map setup" tried
to merge the address map for the four orion platforms, but apparently
got it wrong for mv78xx0. Admittedly I don't understand what this
code actually does, but it's clear that the current version is
wrong.

Without this patch, building mv78xx0_defconfig results in:

arch/arm/mach-mv78xx0/addr-map.c:59:2: warning: initialization from incompatible pointer type [enabled by default]
arch/arm/mach-mv78xx0/addr-map.c:59:2: warning: (near initialization for 'addr_map_cfg.win_cfg_base') [enabled by default]

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Andrew Lunn <andrew@lunn.ch>
Cc: Michael Walle <michael@walle.cc>
Cc: Nicolas Pitre <nico@linaro.org>