sched_ext: Fix missing return after scx_error() in scx_dsq_move()

sched_ext: Fix missing return after scx_error() in scx_dsq_move()

When scx_bpf_dsq_move[_vtime]() is called on a task that belongs to a
different scheduler, scx_error() is invoked to flag the violation.
scx_error() schedules an asynchronous scheduler teardown via irq_work
and returns immediately, so execution falls through and the DSQ move
proceeds on a cross-scheduler task regardless, potentially corrupting
DSQ state.

Add the missing return false so the function exits right after
reporting the error, consistent with the other early-exit checks in
the same function (e.g. scx_vet_enq_flags() failure at the top).

Fixes: bb4d9fd55158 ("sched_ext: scx_dsq_move() should validate the task belongs to the right scheduler")
Signed-off-by: Cheng-Yang Chou <yphbchou0911@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>