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/usb/gadget/composite.c b/drivers/usb/gadget/composite.c
index a13b21d..60f9272 100644
--- a/drivers/usb/gadget/composite.c
+++ b/drivers/usb/gadget/composite.c
@@ -2,7 +2,7 @@
  * composite.c - infrastructure for Composite USB Gadgets
  *
  * Copyright (C) 2006-2008 David Brownell
- * U-boot porting: Lukasz Majewski <l.majewski@samsung.com>
+ * U-Boot porting: Lukasz Majewski <l.majewski@samsung.com>
  *
  * SPDX-License-Identifier:	GPL-2.0+
  */