HWPOISON: Turn addr_valid from bitfield into char

The addr_valid flag is the only flag in "to_kill" and it's slightly more
efficient to have it as char instead of a bitfield.
Signed-off-by: Andi Kleen <ak@linux.intel.com>

mm/memory-failure.c

@@ -272,7 +272,7 @@ struct to_kill {
 	struct list_head nd;
 	struct task_struct *tsk;
 	unsigned long addr;
-	unsigned addr_valid:1;
+	char addr_valid;
 };
 
 /*