Moved sanity check in lfs_format after compaction

After a bit of tweaking in 9dde5c7 to write out all superblocks
during lfs_format, additional writes were added after the sanity
checking normally done at the end.

This turned out to be a problem when porting littlefs, as it makes it
easy for addressing issues to not get caught during lfs_format.

Found by marekr, tristanclare94, and mjs513

lfs.c

@@ -3616,12 +3616,6 @@ static int lfs_rawformat(lfs_t *lfs, const struct lfs_config *cfg) {
             goto cleanup;
         }
 
-        // sanity check that fetch works
-        err = lfs_dir_fetch(lfs, &root, (const lfs_block_t[2]){0, 1});
-        if (err) {
-            goto cleanup;
-        }
-
         // force compaction to prevent accidentally mounting any
         // older version of littlefs that may live on disk
         root.erased = false;
@@ -3629,6 +3623,12 @@ static int lfs_rawformat(lfs_t *lfs, const struct lfs_config *cfg) {
         if (err) {
             goto cleanup;
         }
+
+        // sanity check that fetch works
+        err = lfs_dir_fetch(lfs, &root, (const lfs_block_t[2]){0, 1});
+        if (err) {
+            goto cleanup;
+        }
     }
 
 cleanup: