fix - ensure we don't use bootconsoles after init has been released

Gerd Hoffmann pointed out that my patch from yesterday can lead
to a null pointer dereference if the kernel is booted with no
console, and no earlyprintk defined. This fixes that issue.
Signed-off-by: NRobin Getz <rgetz@blackfin.uclinux.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

kernel/printk.c

@@ -1085,10 +1085,12 @@ EXPORT_SYMBOL(unregister_console);
 
 static int __init disable_boot_consoles(void)
 {
-	if (console_drivers->flags & CON_BOOT) {
-		printk(KERN_INFO "turn off boot console %s%d\n",
-			console_drivers->name, console_drivers->index);
-		return unregister_console(console_drivers);
+	if (console_drivers != NULL) {
+		if (console_drivers->flags & CON_BOOT) {
+			printk(KERN_INFO "turn off boot console %s%d\n",
+				console_drivers->name, console_drivers->index);
+			return unregister_console(console_drivers);
+		}
 	}
 	return 0;
 }