UBIFS: fix the dark space calculation

The dark space calculation should be 64 bit type-casted, when
assigning to tmp64 (similar to how total_free is calculated).
Overflow will occur for very large flashes.
Signed-off-by: srimugunthan <srimugunthan.dhandapani@gmail.com>
Signed-off-by: Artem Bityutskiy <artem.bityutskiy@intel.com>

fs/ubifs/sb.c

@@ -247,7 +247,7 @@ static int create_default_filesystem(struct ubifs_info *c)
 	mst->total_dirty = cpu_to_le64(tmp64);
 
 	/*  The indexing LEB does not contribute to dark space */
-	tmp64 = (c->main_lebs - 1) * c->dark_wm;
+	tmp64 = ((long long)(c->main_lebs - 1) * c->dark_wm);
 	mst->total_dark = cpu_to_le64(tmp64);
 
 	mst->total_used = cpu_to_le64(UBIFS_INO_NODE_SZ);