s390/irq: utilize RCU instead of irq_lock_sparse() in show_msi_interrupt()

As demonstrated by commit 74bdf7815d ("genirq: Speedup
show_interrupts()"), irq_desc can be accessed safely in RCU read section.

Hence here resorting to rcu read lock to get rid of irq_lock_sparse().

Signed-off-by: Pingfan Liu <kernelfans@gmail.com>
Link: https://lore.kernel.org/r/20220422100212.22666-1-kernelfans@gmail.com
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

arch/s390/kernel/irq.c

@@ -205,7 +205,7 @@ static void show_msi_interrupt(struct seq_file *p, int irq)
 	unsigned long flags;
 	int cpu;
 
-	irq_lock_sparse();
+	rcu_read_lock();
 	desc = irq_to_desc(irq);
 	if (!desc)
 		goto out;
@@ -224,7 +224,7 @@ static void show_msi_interrupt(struct seq_file *p, int irq)
 	seq_putc(p, '\n');
 	raw_spin_unlock_irqrestore(&desc->lock, flags);
 out:
-	irq_unlock_sparse();
+	rcu_read_unlock();
 }
 
 /*