Btrfs: fix off by one while setting block groups readonly

When we read in block groups, we'll set non-redundant groups
readonly if we find a raid1, DUP or raid10 group.  But the
ro code has an off by one bug in the math around testing to
make sure out accounting doesn't go wrong.
Signed-off-by: NChris Mason <chris.mason@oracle.com>

fs/btrfs/extent-tree.c

@@ -7971,13 +7971,14 @@ static int set_block_group_ro(struct btrfs_block_group_cache *cache)
 
 	if (sinfo->bytes_used + sinfo->bytes_reserved + sinfo->bytes_pinned +
 	    sinfo->bytes_may_use + sinfo->bytes_readonly +
-	    cache->reserved_pinned + num_bytes < sinfo->total_bytes) {
+	    cache->reserved_pinned + num_bytes <= sinfo->total_bytes) {
 		sinfo->bytes_readonly += num_bytes;
 		sinfo->bytes_reserved += cache->reserved_pinned;
 		cache->reserved_pinned = 0;
 		cache->ro = 1;
 		ret = 0;
 	}
+
 	spin_unlock(&cache->lock);
 	spin_unlock(&sinfo->lock);
 	return ret;