ANDROID: GKI: sched: fix CRC issues related to CONFIG_SCHED_TUNE

Move the new stune_idx to use one of the KABI padding fields.

Bug: 185091725
Fixes: bca62a0a ("sched/tune: Fix improper accounting of tasks")
Signed-off-by: Will McVicker <willmcvicker@google.com>
Change-Id: Ibd31dfc2158a766f1dcb8e63ddc4193dac6d6077