ANDROID: ion: check for kref overflow

Userspace can cause the kref to handles to increment
arbitrarily high. Ensure it does not overflow.

Signed-off-by: Daniel Rosenberg <drosen@google.com>

Bug: 31992382
Test: See bug for poc
Change-Id: I6bff1df385742b1d836d43180dc87fadcea80782
Git-repo: https://android.googlesource.com/kernel/msm


Git-commit: 0c702db4d90de88df11057bcf0d8fb2dfe741605
Signed-off-by: Dennis Cagle <d-cagle@codeaurora.org>