mips: Return proper error code from console ->setup() hook

For unifying console ->setup() handling, which is poorly documented,
return error code, rather than non-zero arbitrary number.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Acked-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20200618164751.56828-2-andriy.shevchenko@linux.intel.com

arch/mips/fw/arc/arc_con.c

@@ -28,7 +28,9 @@ static void prom_console_write(struct console *co, const char *s,
 
 static int prom_console_setup(struct console *co, char *options)
 {
-	return !(prom_flags & PROM_FLAG_USE_AS_CONSOLE);
+	if (prom_flags & PROM_FLAG_USE_AS_CONSOLE)
+		return 0;
+	return -ENODEV;
 }
 
 static struct console arc_cons = {