Move the definition of function in zeroize

There is a static dependency in the test system for
this file. To prevent the issue from happening, move
the definition to the end of file so that the last
return in the main remains in the same line.
diff --git a/programs/test/zeroize.c b/programs/test/zeroize.c
index 6e7db4e..54f7c62 100644
--- a/programs/test/zeroize.c
+++ b/programs/test/zeroize.c
@@ -59,19 +59,6 @@
     mbedtls_printf( "       zeroize <FILE>\n" );
 }
 
-#if defined(MBEDTLS_ENTROPY_HARDWARE_ALT)
-int mbedtls_hardware_poll( void *data, unsigned char *output,
-                           size_t len, size_t *olen )
-{
-    size_t i;
-    (void) data;
-    for( i = 0; i < len; ++i )
-        output[i] = rand();
-    *olen = len;
-    return( 0 );
-}
-#endif
-
 int main( int argc, char** argv )
 {
     int exit_code = MBEDTLS_EXIT_FAILURE;
@@ -112,3 +99,16 @@
 
     return( exit_code );
 }
+
+#if defined(MBEDTLS_ENTROPY_HARDWARE_ALT)
+int mbedtls_hardware_poll( void *data, unsigned char *output,
+                           size_t len, size_t *olen )
+{
+    size_t i;
+    (void) data;
+    for( i = 0; i < len; ++i )
+        output[i] = rand();
+    *olen = len;
+    return( 0 );
+}
+#endif