vvfat: convert to .bdrv_co_is_allocated()

It is trivial to switch from the synchronous .bdrv_is_allocated()
interface to .bdrv_co_is_allocated() since vvfat_is_allocated() does not
block.
Signed-off-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block/vvfat.c

@@ -2758,7 +2758,7 @@ static coroutine_fn int vvfat_co_write(BlockDriverState *bs, int64_t sector_num,
     return ret;
 }
 
-static int vvfat_is_allocated(BlockDriverState *bs,
+static int coroutine_fn vvfat_co_is_allocated(BlockDriverState *bs,
 	int64_t sector_num, int nb_sectors, int* n)
 {
     BDRVVVFATState* s = bs->opaque;
@@ -2855,7 +2855,7 @@ static BlockDriver bdrv_vvfat = {
     .bdrv_read          = vvfat_co_read,
     .bdrv_write         = vvfat_co_write,
     .bdrv_close		= vvfat_close,
-    .bdrv_is_allocated	= vvfat_is_allocated,
+    .bdrv_co_is_allocated = vvfat_co_is_allocated,
     .protocol_name	= "fat",
 };