mtd: external toolchains usually do not know about MTDREFRESH, so search in $(LINUX_DIR)/include first, fixes compilation with external CodeSourcery toolchain

SVN-Revision: 29779

package/mtd/Makefile

@@ -35,7 +35,7 @@ endef
 target=$(firstword $(subst -, ,$(BOARD)))
 
 MAKE_FLAGS += TARGET="$(target)"
-TARGET_CFLAGS += -Dtarget_$(target)=1 -Wall
+TARGET_CFLAGS := -I$(LINUX_DIR)/include $(TARGET_CFLAGS) -Dtarget_$(target)=1 -Wall
 
 ifdef CONFIG_MTD_REDBOOT_PARTS
   MAKE_FLAGS += FIS_SUPPORT=1