Prevented unnecessary superblock rewrites if old version in superblock chain

Because multiple, out-of-date superblocks can exist in our superblock
chain, we need to be careful to make sure newer superblock entries
override older superblock entries.

If we see an older on-disk minor version in the superblock chain, we
were correctly overriding the on-disk minor version, but we were also
leaving the "needs superblock" bit set in our consistency state.

This isn't a hard-error, but would lead to a superblock rewrite every
mount. The rewrite would make no progress, as the out-of-date version is
effectively immutable at this point, and just waste prog cycles.

This should fix that by clearing the "needs superblock" bit if we see a
newer on-disk minor version.

lfs.c

diff --git a/lfs.c b/lfs.c
index 4e4dd9b..0e62b5f 100644
--- a/lfs.c
+++ b/lfs.c
@@ -4469,6 +4469,7 @@
             // found older minor version? set an in-device only bit in the
             // gstate so we know we need to rewrite the superblock before
             // the first write
+            bool needssuperblock = false;
             if (minor_version < lfs_fs_disk_version_minor(lfs)) {
                 LFS_DEBUG("Found older minor version "
                         "v%"PRIu16".%"PRIu16" < v%"PRIu16".%"PRIu16,
@@ -4476,10 +4477,11 @@
                         minor_version,
                         lfs_fs_disk_version_major(lfs),
                         lfs_fs_disk_version_minor(lfs));
-                // note this bit is reserved on disk, so fetching more gstate
-                // will not interfere here
-                lfs_fs_prepsuperblock(lfs, true);
+                needssuperblock = true;
             }
+            // note this bit is reserved on disk, so fetching more gstate
+            // will not interfere here
+            lfs_fs_prepsuperblock(lfs, needssuperblock);
 
             // check superblock configuration
             if (superblock.name_max) {