ide: remove undefined behavior in ide-test

trivial: initialize the dirty buffer with a random-ish byte.
Stops valgrind from whining about uninitialized buffers.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

tests/ide-test.c

@@ -544,6 +544,7 @@ static void make_dirty(uint8_t device)
 
     guest_buf = guest_alloc(guest_malloc, len);
     buf = g_malloc(len);
+    memset(buf, rand() % 255 + 1, len);
     g_assert(guest_buf);
     g_assert(buf);