console/vsprintf.c: Add <stdarg.h>

Signed-off-by: Elyes Haouas <ehaouas@noos.fr>
Change-Id: I8c61f2a033f9630d3fa3eb5e364e6f38de5c7064
Reviewed-on: https://review.coreboot.org/c/coreboot/+/68038
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Martin L Roth <gaumless@gmail.com>

src/console/vsprintf.c

@@ -1,6 +1,7 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 
 #include <console/vtxprintf.h>
+#include <stdarg.h>
 #include <string.h>
 
 struct vsnprintf_context {