powerpc/8xxx: Fix compile warning when build for a DDR1 or DDR2 board

ctrl_regs.c: In function 'set_ddr_sdram_mode_2':
ctrl_regs.c:690:6: warning: unused variable 'i'

'i' is only used by DDR3 code.
Signed-off-by: NKumar Gala <galak@kernel.crashing.org>

arch/powerpc/cpu/mpc8xxx/ddr/ctrl_regs.c

@@ -687,9 +687,9 @@ static void set_ddr_sdram_mode_2(fsl_ddr_cfg_regs_t *ddr,
 {
 	unsigned short esdmode2 = 0;	/* Extended SDRAM mode 2 */
 	unsigned short esdmode3 = 0;	/* Extended SDRAM mode 3 */
-	int i;
 
 #if defined(CONFIG_FSL_DDR3)
+	int i;
 	unsigned int rtt_wr = 0;	/* Rtt_WR - dynamic ODT off */
 	unsigned int srt = 0;	/* self-refresh temerature, normal range */
 	unsigned int asr = 0;	/* auto self-refresh disable */