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/arch/arm/mach-exynos/spl_boot.c b/arch/arm/mach-exynos/spl_boot.c
index c7f943e..7df0102 100644
--- a/arch/arm/mach-exynos/spl_boot.c
+++ b/arch/arm/mach-exynos/spl_boot.c
@@ -177,7 +177,7 @@
 #endif
 
 /*
-* Copy U-boot from mmc to RAM:
+* Copy U-Boot from mmc to RAM:
 * COPY_BL2_FNPTR_ADDR: Address in iRAM, which Contains
 * Pointer to API (Data transfer from mmc to ram)
 */