util: change coreboot to lowercase

The word 'coreboot' should always be written in lowercase, even at the
start of a sentence.

Change-Id: I0a024d82d331c0794fe087e440b4e1924129a13c
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/20030
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>

util/nvramtool/cmos_ops.c

@@ -227,7 +227,7 @@ void cmos_checksum_verify(void)
 	set_iopl(0);
 
 	if (computed != actual) {
-		fprintf(stderr, "%s: Warning: Coreboot CMOS checksum is bad.\n",
+		fprintf(stderr, "%s: Warning: coreboot CMOS checksum is bad.\n",
 			prog_name);
 		fprintf(stderr, "Computed checksum: 0x%x. Stored checksum: 0x%x\n",
 			computed, actual);