trivial: fix typos in comments s/DGBU/DBGU/

DBGU means Debug Unit, was refered as "DGBU" in some files. Fixed to "DBGU".

Signed-off-by: Samuel R. C. Vale <srcvale@holoscopio.com>
Acked-by: Andrew Victor <linux@maxim.org.za>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

arch/arm/mach-at91/board-sam9263ek.c

@@ -57,7 +57,7 @@ static void __init ek_map_io(void)
 	/* Initialize processor: 16.367 MHz crystal */
 	at91sam9263_initialize(16367660);
 
-	/* DGBU on ttyS0. (Rx & Tx only) */
+	/* DBGU on ttyS0. (Rx & Tx only) */
 	at91_register_uart(0, 0, 0);
 
 	/* USART0 on ttyS1. (Rx, Tx, RTS, CTS) */