powerpc/irq: Simplify __do_irq()

Remove duplicated code by implementing a proper if/else.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/5a3b21311191f1240850db6ab29b19ac7885fe03.1654769775.git.christophe.leroy@csgroup.eu

arch/powerpc/kernel/irq.c

@@ -281,14 +281,11 @@ void __do_IRQ(struct pt_regs *regs)
 	irqsp = hardirq_ctx[raw_smp_processor_id()];
 	sirqsp = softirq_ctx[raw_smp_processor_id()];
 
-	/* Already there ? */
-	if (unlikely(cursp == irqsp || cursp == sirqsp)) {
+	/* Already there ? If not switch stack and call */
+	if (unlikely(cursp == irqsp || cursp == sirqsp))
 		__do_irq(regs, current_stack_pointer);
-		set_irq_regs(old_regs);
-		return;
-	}
-	/* Switch stack and call */
-	call_do_irq(regs, irqsp);
+	else
+		call_do_irq(regs, irqsp);
 
 	set_irq_regs(old_regs);
 }