sched: Remove never used code in mm_cid_get()

Clang is not happy with set but unused variable (this is visible
with `make W=1` build:

  kernel/sched/sched.h:3744:18: error: variable 'cpumask' set but not used [-Werror,-Wunused-but-set-variable]

It seems like the variable was never used along with the assignment
that does not have side effects as far as I can see.  Remove those
altogether.

Fixes: 223baf9 ("sched: Fix performance regression introduced by mm_cid")
Signed-off-by: Andy Shevchenko <[email protected]>
Tested-by: Eric Biggers <[email protected]>
Reviewed-by: Breno Leitao <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Author: andy-shev

kernel/sched/sched.h

@@ -3740,11 +3740,9 @@ static inline int mm_cid_get(struct rq *rq, struct task_struct *t,
 			     struct mm_struct *mm)
 {
 	struct mm_cid __percpu *pcpu_cid = mm->pcpu_cid;
-	struct cpumask *cpumask;
 	int cid;
 
 	lockdep_assert_rq_held(rq);
-	cpumask = mm_cidmask(mm);
 	cid = __this_cpu_read(pcpu_cid->cid);
 	if (mm_cid_is_valid(cid)) {
 		mm_cid_snapshot_time(rq, mm);