ANDROID: uid_sys_stats: Fully initialize uid_entry_tmp value

Amit Pundir at Linaro reported seeing crashes in uid_sys_stats
driver when building with GCC.

Looking into it, it seems the uid_entry_tmp value is used
while only partially initialized, causing potential out of bound
access on the uid_entry io arrays.

This likely has gone unnoticed with clang as I believe we're
using the zero initialization for stack variables security
feature.

So change the logic to fully initialize the uid_entry_tmp
value.

Fixes: f68d4f3c ("ANDROID: uid_sys_stat: instead update_io_stats_uid_locked to update_io_stats_uid")
Reported-by: Amit Pundir <amit.pundir@linaro.org>
Signed-off-by: John Stultz <jstultz@google.com>
Change-Id: I78de245e80ef60aabec78a615c7ba582ab5a2242