Revert "block/io: Comment out permission assertions"

This reverts commit e3e0003a8f6570aba1421ef99a0b383a43371a74.

This commit was necessary for the 2.9 release because we were unable to
fix the underlying issue(s) in time. However, we will be for 2.10.

Signed-off-by: Max Reitz <mreitz@redhat.com>
Acked-by: Fam Zheng <famz@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
diff --git a/block.c b/block.c
index 5db266b..ceaca44 100644
--- a/block.c
+++ b/block.c
@@ -3313,11 +3313,7 @@
     BlockDriver *drv = bs->drv;
     int ret;
 
-    /* FIXME: Some format block drivers use this function instead of implicitly
-     *        growing their file by writing beyond its end.
-     *        See bdrv_aligned_pwritev() for an explanation why we currently
-     *        cannot assert this permission in that case. */
-    // assert(child->perm & BLK_PERM_RESIZE);
+    assert(child->perm & BLK_PERM_RESIZE);
 
     if (!drv)
         return -ENOMEDIUM;