sched/core: Fix uninitialized variable used for tracepoint

When predictive dcvs is enabled a tracepoint will log a value that is
garbage due to being uninitialized. Fix this.

CRs-fixed: 1042660
Change-Id: I2b94e78f2470dbc2fd469b5cab287d643e8f3227
Signed-off-by: Olav Haugan <ohaugan@codeaurora.org>