Use GCC_FMT_ATTR (format checking)

Signed-off-by: Stefan Weil <weil@mail.berlios.de>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
diff --git a/hw/mips_malta.c b/hw/mips_malta.c
index 1cb7880..09690894 100644
--- a/hw/mips_malta.c
+++ b/hw/mips_malta.c
@@ -654,7 +654,8 @@
 
 }
 
-static void prom_set(uint32_t* prom_buf, int index, const char *string, ...)
+static void GCC_FMT_ATTR(3, 4) prom_set(uint32_t* prom_buf, int index,
+                                        const char *string, ...)
 {
     va_list ap;
     int32_t table_addr;