avutil/sha512-test: fix memleak

Signed-off-by: James Almer <jamrial@gmail.com>

libavutil/sha512-test.c

@@ -23,6 +23,7 @@
 
 #include <stdio.h>
 
+#include "mem.h"
 #include "sha512.h"
 
 int main(void)
@@ -83,6 +84,7 @@ int main(void)
             break;
         }
     }
+    av_free(ctx);
 
     return 0;
 }