Include <stdlib.h> for the malloc function.

Submitted upstream: <https://github.com/dfu-programmer/dfu-programmer/pull/76>

diff --git a/src/atmel.c b/src/atmel.c
index 4ea794d17f65d8d0..491bbb16706e65a8 100644
--- a/src/atmel.c
+++ b/src/atmel.c
@@ -19,6 +19,7 @@
  */
 
 #include <stdio.h>
+#include <stdlib.h>
 #include <stdarg.h>
 #include <stdint.h>
 #include <string.h>