ion: fix crash when alloc len is -1

If userspace passes a length between -4095 and -1 to allocate it
will pass the len != 0 check, but when len is page aligned it will
be 0.  Check len after page aligning.

Drop the warning as well, userspace shouldn't be able to trigger
a warning in the kernel.

Signed-off-by: Colin Cross <ccross@android.com>
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/android/ion/ion.c

@@ -485,11 +485,11 @@ struct ion_handle *ion_alloc(struct ion_client *client, size_t len,
 	 * request of the caller allocate from it.  Repeat until allocate has
 	 * succeeded or all heaps have been tried
 	 */
-	if (WARN_ON(!len))
-		return ERR_PTR(-EINVAL);
-
 	len = PAGE_ALIGN(len);
 
+	if (!len)
+		return ERR_PTR(-EINVAL);
+
 	down_read(&dev->lock);
 	plist_for_each_entry(heap, &dev->heaps, node) {
 		/* if the caller didn't specify this heap id */