Fix return value of lfs_rename()

When lfs_rename() is called trying to rename (move) a file to an
existing directory, LFS_ERR_ISDIR is (correctly) returned. However, in
the opposite case, if one tries to rename (move) a directory to a path
currently occupied by a regular file, LFS_ERR_NOTDIR should be
returned (since the error is that the destination is NOT a directory),
but in reality, LFS_ERR_ISDIR is returned in this case as well.

This commit fixes the code so that in the latter case, LFS_ERR_NOTDIR
is returned.

lfs.c

@@ -3940,7 +3940,9 @@ static int lfs_rawrename(lfs_t *lfs, const char *oldpath, const char *newpath) {
             newoldid += 1;
         }
     } else if (lfs_tag_type3(prevtag) != lfs_tag_type3(oldtag)) {
-        return LFS_ERR_ISDIR;
+        return (lfs_tag_type3(prevtag) == LFS_TYPE_DIR)
+                ? LFS_ERR_ISDIR
+                : LFS_ERR_NOTDIR;
     } else if (samepair && newid == newoldid) {
         // we're renaming to ourselves??
         return 0;