m68k: mac: Remove forward declaration for mac_nmi_handler()

Move mac_nmi_handler() before its caller, so its forward declaration can
be dropped.  While at it, make the function static, and absorb the
variable in_nmi, which is only used inside the function.

Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Finn Thain <fthain@linux-m68k.org>
Link: https://lore.kernel.org/r/fa48394ecba7c29a2da354d13c1017b37237f25b.1657114783.git.geert@linux-m68k.org

Author: geertu

arch/m68k/mac/macints.c

@@ -129,8 +129,6 @@
 
 extern void show_registers(struct pt_regs *);
 
-irqreturn_t mac_nmi_handler(int, void *);
-
 static unsigned int mac_irq_startup(struct irq_data *);
 static void mac_irq_shutdown(struct irq_data *);
 
@@ -142,6 +140,21 @@ static struct irq_chip mac_irq_chip = {
 	.irq_shutdown	= mac_irq_shutdown,
 };
 
+static irqreturn_t mac_nmi_handler(int irq, void *dev_id)
+{
+	static volatile int in_nmi;
+
+	if (in_nmi)
+		return IRQ_HANDLED;
+	in_nmi = 1;
+
+	pr_info("Non-Maskable Interrupt\n");
+	show_registers(get_irq_regs());
+
+	in_nmi = 0;
+	return IRQ_HANDLED;
+}
+
 void __init mac_init_IRQ(void)
 {
 	m68k_setup_irq_controller(&mac_irq_chip, handle_simple_irq, IRQ_USER,
@@ -254,18 +267,3 @@ static void mac_irq_shutdown(struct irq_data *data)
 	else
 		mac_irq_disable(data);
 }
-
-static volatile int in_nmi;
-
-irqreturn_t mac_nmi_handler(int irq, void *dev_id)
-{
-	if (in_nmi)
-		return IRQ_HANDLED;
-	in_nmi = 1;
-
-	pr_info("Non-Maskable Interrupt\n");
-	show_registers(get_irq_regs());
-
-	in_nmi = 0;
-	return IRQ_HANDLED;
-}