flashrom: fix gcc5 build

default C dialect changed with gcc5
explicitly use old C dialect

Signed-off-by: Dirk Neukirchen <dirkneukirchen@web.de>

utils/flashrom/Makefile

@@ -46,6 +46,8 @@ define Package/flashrom/description
  /firmware images.
 endef
 
+TARGET_CFLAGS+=-std=gnu89
+
 MAKE_FLAGS += \
 	PREFIX="/usr"