ELOG: Fix warning to fix the compilation.

Without that fix we have:
  src/drivers/elog/elog.c: In function 'elog_is_header_valid':
  src/drivers/elog/elog.c:213:3: error: format '%u' expects argument of type 'unsigned int', but argument 4 has type 'long unsigned int' [-Werror=format]

Change-Id: I71b80a94c03a04eedb688ae107d92c05a878315e
Signed-off-by: Denis 'GNUtoo' Carikli <GNUtoo@no-log.org>
Reviewed-on: http://review.coreboot.org/3551
Reviewed-by: Nico Huber <nico.huber@secunet.com>
Tested-by: build bot (Jenkins)
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
diff --git a/src/drivers/elog/elog.c b/src/drivers/elog/elog.c
index 1a794d9..71e908b 100644
--- a/src/drivers/elog/elog.c
+++ b/src/drivers/elog/elog.c
@@ -210,7 +210,7 @@
 		return 0;
 	}
 	if (header->header_size != sizeof(*header)) {
-		printk(BIOS_ERR, "ELOG: header size mismatch %u != %u\n",
+		printk(BIOS_ERR, "ELOG: header size mismatch %u != %zu\n",
 		       header->header_size, sizeof(*header));
 		return 0;
 	}