ipc/sem.c: spelling fix

s/purpuse/purpose/

Link: https://lkml.kernel.org/r/[e-mail]
Signed-off-by: Bhaskar Chowdhury <[e-mail]>
Acked-by: Randy Dunlap <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

ipc/sem.c

···
 {
 	get_task_struct(q->sleeper);
 
-	/* see SEM_BARRIER_2 for purpuse/pairing */
+	/* see SEM_BARRIER_2 for purpose/pairing */
 	smp_store_release(&q->status, error);
 
 	wake_q_add_safe(wake_q, q->sleeper);