util/nvidia: Use c11 dialect

Change-Id: I75909ce85eed549d9094ba6f62d93656621d9f0d
Signed-off-by: Elyes Haouas <ehaouas@noos.fr>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/82679
Reviewed-by: Felix Singer <service+coreboot-gerrit@felixsinger.de>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
diff --git a/util/nvidia/Makefile.mk b/util/nvidia/Makefile.mk
index 04199d0..08cdfc1 100644
--- a/util/nvidia/Makefile.mk
+++ b/util/nvidia/Makefile.mk
@@ -42,7 +42,7 @@
 
 CBOOTIMAGE_SRCS:=$(addprefix util/nvidia/cbootimage/src/,$(filter %.c,$(CBOOTIMAGE_RAW_SRCS)))
 CBOOTIMAGE_OBJS:=$(addprefix $(objutil)/nvidia/cbootimage/,$(patsubst %.c,%.o,$(filter %.c,$(CBOOTIMAGE_RAW_SRCS))))
-CBOOTIMAGE_FLAGS:=-Wall -std=c99 -O2
+CBOOTIMAGE_FLAGS:=-Wall -std=c11 -O2
 
 ifeq ($(OS_ARCH), FreeBSD)
 CBOOTIMAGE_FLAGS:=-DENODATA=ENOATTR