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/net/e1000.c b/drivers/net/e1000.c
index 70fc02e..6a434d7 100644
--- a/drivers/net/e1000.c
+++ b/drivers/net/e1000.c
@@ -5380,7 +5380,7 @@
 	for (i = 0; (devno = pci_find_devices(e1000_supported, i)) >= 0; i++) {
 		/*
 		 * These will never get freed due to errors, this allows us to
-		 * perform SPI EEPROM programming from U-boot, for example.
+		 * perform SPI EEPROM programming from U-Boot, for example.
 		 */
 		struct eth_device *nic = malloc(sizeof(*nic));
 		struct e1000_hw *hw = malloc(sizeof(*hw));