serial: 8250_platform: Explicitly show we initialise ISA ports only once

serial8250_isa_init_ports() uses home grown approach to make itself
a singleton. Instead, explicitly show that we initialise ISA ports
once by providing a helper function which calls the original function
via DO_ONCE() macro.

Signed-off-by: Andy Shevchenko <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/tty/serial/8250/8250_platform.c

···
 #include <linux/array_size.h>
 #include <linux/module.h>
 #include <linux/moduleparam.h>
+#include <linux/once.h>
 #include <linux/platform_device.h>
 
 #include <linux/serial_8250.h>
···
 }
 EXPORT_SYMBOL(serial8250_set_isa_configurator);
 
-void __init serial8250_isa_init_ports(void)
+static void __init __serial8250_isa_init_ports(void)
 {
-	static int first = 1;
 	int i, irqflag = 0;
-
-	if (!first)
-		return;
-	first = 0;
 
 	if (nr_uarts > UART_NR)
 		nr_uarts = UART_NR;
···
 
 		serial_base_add_isa_preferred_console(serial8250_reg.dev_name, i);
 	}
+}
+
+void __init serial8250_isa_init_ports(void)
+{
+	DO_ONCE(__serial8250_isa_init_ports);
 }
 
 /*