drivers/elog: Use format string

clang shows the warning below:

src/drivers/elog/elog.c:171:13: error:
format string is not a string literal
(potentially insecure) [-Werror,-Wformat-security]
            elog_debug(msg);
                       ^~~

Found-by: clang (13.0.1)
Change-Id: I3f8949f9ce0c4ef4823530c61c503b0883bb5efc
Signed-off-by: Matei Dibu <matdibu@protonmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/66262
Reviewed-by: Paul Menzel <paulepanter@mailbox.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Matt DeVillier <matt.devillier@gmail.com>

src/drivers/elog/elog.c

@@ -168,7 +168,7 @@ static void elog_debug_dump_buffer(const char *msg)
 	if (!CONFIG(ELOG_DEBUG))
 		return;
 
-	elog_debug(msg);
+	elog_debug("%s", msg);
 
 	rdev = mirror_dev_get();