examples/Makefile.am: rename callback/prolog to callback/prologue

examples/Makefile.am

@@ -257,7 +257,7 @@ STARPU_EXAMPLES +=				\
 	spmd/vector_scal_spmd			\
 	spmv/spmv				\
 	callback/callback			\
-	callback/prolog		\
+	callback/prologue			\
 	incrementer/incrementer			\
 	binary/binary				\
 	interface/complex			\