bump version to 1.15.3

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/Makefile b/Makefile
index 7529cd8..ee31906 100644
--- a/Makefile
+++ b/Makefile
@@ -1,6 +1,6 @@
 VERSION = 1
 PATCHLEVEL = 15
-SUBLEVEL = 2
+SUBLEVEL = 3
 EXTRAVERSION =
 NAME = Unnamed