printk: fix name/type/scope of preferred_console var

The variable preferred_console is used only inside register_console()
and its semantics is boolean.  It is negative when no console has been
made preferred.

Make it static bool and rename to has_preferred.

Renaming was suggested by Peter Hurley

Link: http://lkml.kernel.org/r/20170315102854.1763-2-aleksey.makarov@linaro.org
Cc: Sudeep Holla <sudeep.holla@arm.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Peter Hurley <peter@hurleysoftware.com>
Cc: Jiri Slaby <jslaby@suse.com>
Cc: Robin Murphy <robin.murphy@arm.com>
Cc: "Nair, Jayachandran" <Jayachandran.Nair@cavium.com>
Cc: linux-serial@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Aleksey Makarov <aleksey.makarov@linaro.org>
Reviewed-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Signed-off-by: Petr Mladek <pmladek@suse.com>

kernel/printk/printk.c

@@ -268,7 +268,6 @@ static struct console *exclusive_console;
 static struct console_cmdline console_cmdline[MAX_CMDLINECONSOLES];
 
 static int selected_console = -1;
-static int preferred_console = -1;
 int console_set_on_cmdline;
 EXPORT_SYMBOL(console_set_on_cmdline);
 
@@ -2411,6 +2410,7 @@ void register_console(struct console *newcon)
 	unsigned long flags;
 	struct console *bcon = NULL;
 	struct console_cmdline *c;
+	static bool has_preferred;
 
 	if (console_drivers)
 		for_each_console(bcon)
@@ -2437,23 +2437,23 @@ void register_console(struct console *newcon)
 	if (console_drivers && console_drivers->flags & CON_BOOT)
 		bcon = console_drivers;
 
-	if (preferred_console < 0 || bcon || !console_drivers)
-		preferred_console = selected_console;
+	if (!has_preferred || bcon || !console_drivers)
+		has_preferred = selected_console >= 0;
 
 	/*
 	 *	See if we want to use this console driver. If we
 	 *	didn't select a console we take the first one
 	 *	that registers here.
 	 */
-	if (preferred_console < 0) {
+	if (!has_preferred) {
 		if (newcon->index < 0)
 			newcon->index = 0;
 		if (newcon->setup == NULL ||
 		    newcon->setup(newcon, NULL) == 0) {
 			newcon->flags |= CON_ENABLED;
 			if (newcon->device) {
 				newcon->flags |= CON_CONSDEV;
-				preferred_console = 0;
+				has_preferred = true;
 			}
 		}
 	}
@@ -2488,7 +2488,7 @@ void register_console(struct console *newcon)
 		newcon->flags |= CON_ENABLED;
 		if (i == selected_console) {
 			newcon->flags |= CON_CONSDEV;
-			preferred_console = selected_console;
+			has_preferred = true;
 		}
 		break;
 	}