selinux: fix spelling error

Fix spelling error in selinux module comments that were identified
using the codespell tool.
No functional changes - documentation only.

Signed-off-by: Tanya Agarwal <tanyaagarwal25699@gmail.com>
Reviewed-by: Mimi Zohar <zohar@linux.ibm.com>
Signed-off-by: Paul Moore <paul@paul-moore.com>

Author: TanyaAgarwal25

security/selinux/avc.c

@@ -936,7 +936,7 @@ static void avc_flush(void)
 
 		spin_lock_irqsave(lock, flag);
 		/*
-		 * With preemptable RCU, the outer spinlock does not
+		 * With preemptible RCU, the outer spinlock does not
 		 * prevent RCU grace periods from ending.
 		 */
 		rcu_read_lock();