ion: ion_system_heap: Fix variable initialization

This patch initialize the variable 'ret' to avoid getting any
random value when CONFIG_MSM_GVM_QUIN is disabled.

Change-Id: I14c0d43a4afd2a9db61237f5a6881e3c638731a6
Signed-off-by: Manohar Vavilapalli <mvavilap@codeaurora.org>