Fix win32 build

Fix a return value change missed by
205ef7961f781496366e0a93a4ec621ad3724bd7.

Signed-off-by: Blue Swirl <blauwirbel@gmail.com>

block/raw-win32.c

@@ -147,7 +147,7 @@ static int raw_write(BlockDriverState *bs, int64_t sector_num,
     return ret_count;
 }
 
-static void raw_flush(BlockDriverState *bs)
+static int raw_flush(BlockDriverState *bs)
 {
     BDRVRawState *s = bs->opaque;
     int ret;