drivers: soc: qcom: Add error handling in function avtimer_ioctl

Error handling is added to prevent garbage value being passed to
user space by the uninitialized local variable avtimer_tick.

CRs-Fixed: 1097878
References: CVE-2016-5346
Change-Id: I3f895deaae3acf329088cf8135859cc41e781763
Signed-off-by: Xiaoyu Ye <benyxy@codeaurora.org>