Use correct spelling of "U-Boot"

Correct spelling of "U-Boot" shall be used in all written text
(documentation, comments in source files etc.).

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Heiko Schocher <hs@denx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Minkyu Kang <mk7.kang@samsung.com>
diff --git a/drivers/ddr/marvell/axp/ddr3_hw_training.c b/drivers/ddr/marvell/axp/ddr3_hw_training.c
index a8c5e6a..c8d7041 100644
--- a/drivers/ddr/marvell/axp/ddr3_hw_training.c
+++ b/drivers/ddr/marvell/axp/ddr3_hw_training.c
@@ -450,7 +450,7 @@
 	ddr3_set_performance_params(&dram_info);
 
 	if (dram_info.ecc_ena) {
-		/* Need to SCRUB the DRAM memory area to load U-boot */
+		/* Need to SCRUB the DRAM memory area to load U-Boot */
 		mv_sys_xor_finish();
 		dram_info.num_cs = 1;
 		dram_info.cs_ena = 1;