block: Convert bdrv_pwrite(v/_sync) to BdrvChild

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Max Reitz <mreitz@redhat.com>
Acked-by: Stefan Hajnoczi <stefanha@redhat.com>
diff --git a/block/vhdx-log.c b/block/vhdx-log.c
index 1e3928f..02eb104 100644
--- a/block/vhdx-log.c
+++ b/block/vhdx-log.c
@@ -194,7 +194,7 @@
             /* full */
             break;
         }
-        ret = bdrv_pwrite(bs->file->bs, offset, buffer_tmp,
+        ret = bdrv_pwrite(bs->file, offset, buffer_tmp,
                           VHDX_LOG_SECTOR_SIZE);
         if (ret < 0) {
             goto exit;
@@ -466,7 +466,7 @@
 
     /* count is only > 1 if we are writing zeroes */
     for (i = 0; i < count; i++) {
-        ret = bdrv_pwrite_sync(bs->file->bs, file_offset, buffer,
+        ret = bdrv_pwrite_sync(bs->file, file_offset, buffer,
                                VHDX_LOG_SECTOR_SIZE);
         if (ret < 0) {
             goto exit;