Blackfin arch: fix unused warning for some blackfin derivatives

Signed-off-by: Mike Frysinger <vapier.adi@gmail.com>
Signed-off-by: Bryan Wu <cooloney@kernel.org>

arch/blackfin/mm/sram-alloc.c

@@ -106,7 +106,9 @@ static void __init l1sram_init(void)
 
 static void __init l1_data_sram_init(void)
 {
+#if L1_DATA_A_LENGTH != 0 || L1_DATA_B_LENGTH != 0
 	unsigned int cpu;
+#endif
 #if L1_DATA_A_LENGTH != 0
 	for (cpu = 0; cpu < num_possible_cpus(); ++cpu) {
 		per_cpu(free_l1_data_A_sram_head, cpu).next =