ANDROID: uid_sys_stat: instead update_io_stats_uid_locked to update_io_stats_uid

Update_io_stats_uid_locked would take a long lock-time of uid_lock due to
call do_each_thread to compute uid_entry->io, which would cause to lock
competition sometime.

Using uid_entry_tmp to get the result of update_io_stats_uid, so that we
can unlock_uid during update_io_stats_uid, in order to avoid the
unnecessary lock-time of uid_lock.

Bug: 278138377

Signed-off-by: Peifeng Li <lipeifeng@oppo.com>
Change-Id: I5be62105e57e2a896a95d906e3c14e17c7f8077d