Use ${MAKE} variable for recursive Makefile

Makefile

@@ -1,5 +1,9 @@
 CFLAGS = -O3 std=c99 -Wall -D_POSIX_C_SOURCE=200809L
 
 all:
-	@make -C tiff
-	@make -C hdf5
+	@${MAKE} -C tiff
+	@${MAKE} -C hdf5
+
+clean:
+	@${MAKE} -C tiff clean
+	@${MAKE} -C hdf5 clean