microblaze: Fix "kstack=" parsing

The "kstack=" command line parameter is not parsed correctly.
All proper values are interpreted as zero.

Signed-off-by: Steven J. Magnani <steve@digidescorp.com>
Signed-off-by: Michal Simek <monstr@monstr.eu>

arch/microblaze/kernel/traps.c

@@ -22,13 +22,11 @@ void trap_init(void)
 	__enable_hw_exceptions();
 }
 
-static int kstack_depth_to_print = 24;
+static unsigned long kstack_depth_to_print = 24;
 
 static int __init kstack_setup(char *s)
 {
-	kstack_depth_to_print = strict_strtoul(s, 0, NULL);
-
-	return 1;
+	return !strict_strtoul(s, 0, &kstack_depth_to_print);
 }
 __setup("kstack=", kstack_setup);