ion: change ion_user_handle_t definition to int

Turn ion_user_handle_t to int. This change reflects the underlying type
returned by the ion driver.

Signed-off-by: Rom Lemarchand <romlem@google.com>
[jstultz: modified patch to apply to staging directory]
Signed-off-by: John Stultz <john.stultz@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>