regmap: Export regcache_sync_region()

regcache_sync_region() isn't going to be useful to most drivers if we
don't export it since otherwise they can't use it when built modular.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>

drivers/base/regmap/regcache.c

@@ -346,6 +346,7 @@ out:
 
 	return ret;
 }
+EXPORT_SYMBOL_GPL(regcache_sync_region);
 
 /**
  * regcache_cache_only: Put a register map into cache only mode