nvramtool: Print computed and stored checksum in case of mismatch.

This is to make it easier to fix checksum issues. Example:
  # nvramtool -a
  [...]
  nvramtool: Warning: Coreboot CMOS checksum is bad.
  Computed checksum: 0xfa. Stored checksum: 0x0
  # nvramtool -c 0xfa

Change-Id: Ifacb68b5693afbdfcb521acd6937e270ead85186
Signed-off-by: Denis 'GNUtoo' Carikli <GNUtoo@no-log.org>
Reviewed-on: https://review.coreboot.org/13770
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>

util/nvramtool/cmos_ops.c

@@ -229,6 +229,8 @@ void cmos_checksum_verify(void)
 	if (computed != actual) {
 		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);
 		exit(1);
 	}
 }