dumpstack: x86: add "end" parameter to valid_stack_ptr and print_context_stack

- Add "end" parameter to valid_stack_ptr and print_context_stack
 - use sizeof(long) as the size of a word on the stack

Signed-off-by: Alexander van Heukelum <heukelum@fastmail.fm>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c
index 563554c..361afa8 100644
--- a/arch/x86/kernel/dumpstack_64.c
+++ b/arch/x86/kernel/dumpstack_64.c
@@ -141,7 +141,7 @@
 
 		addr = *stack;
 		if (__kernel_text_address(addr)) {
-			if ((unsigned long) stack == bp + 8) {
+			if ((unsigned long) stack == bp + sizeof(long)) {
 				ops->address(data, addr, 1);
 				frame = frame->next_frame;
 				bp = (unsigned long) frame;