MIPS: ralink: export rt_sysc_membase for rt2880_wdt.c

rt2880_wdt.c uses (well, attempts to use) rt_sysc_membase. However,
when this watchdog driver is built as a loadable module, there is a
build error since the rt_sysc_membase symbol is not exported.
Export it to quell the build error.

ERROR: modpost: "rt_sysc_membase" [drivers/watchdog/rt2880_wdt.ko] undefined!

Fixes: 473cf939ff ("watchdog: add ralink watchdog driver")
Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Wim Van Sebroeck <wim@iguana.be>
Cc: John Crispin <john@phrozen.org>
Cc: linux-mips@vger.kernel.org
Cc: linux-watchdog@vger.kernel.org
Acked-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/ralink/of.c

@@ -8,6 +8,7 @@
 
 #include <linux/io.h>
 #include <linux/clk.h>
+#include <linux/export.h>
 #include <linux/init.h>
 #include <linux/sizes.h>
 #include <linux/of_fdt.h>
@@ -25,6 +26,7 @@
 
 __iomem void *rt_sysc_membase;
 __iomem void *rt_memc_membase;
+EXPORT_SYMBOL_GPL(rt_sysc_membase);
 
 __iomem void *plat_of_remap_node(const char *node)
 {