omap: fix a gpmc nand problem

If gpmc_t isn't given, we don't need to set timing for gpmc, or it will cause
a Oops.
Signed-off-by: Stanley.Miao <stanley.miao@windriver.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>

arch/arm/mach-omap2/gpmc-nand.c

@@ -39,6 +39,9 @@ static int omap2_nand_gpmc_retime(void)
 	struct gpmc_timings t;
 	int err;
 
+	if (!gpmc_nand_data->gpmc_t)
+		return 0;
+
 	memset(&t, 0, sizeof(t));
 	t.sync_clk = gpmc_round_ns_to_ticks(gpmc_nand_data->gpmc_t->sync_clk);
 	t.cs_on = gpmc_round_ns_to_ticks(gpmc_nand_data->gpmc_t->cs_on);