s390/dumpstack: get rid of return_address again

With commit ef6000b4c670 ("Disable the __builtin_return_address()
warning globally after all)" the kernel does not warn at all again if
__builtin_return_address(n) is called with n > 0.

Besides the fact that this was a false warning on s390 anyway, due to
the always present backchain, we can now revert commit 5606330627ab
("s390/dumpstack: implement and use return_address()") again, to
simplify the code again.

After all I shouldn't have had return_address() implememted at all to
workaround this issue. So get rid of this again.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/ftrace.h

@@ -12,9 +12,7 @@
 
 #ifndef __ASSEMBLY__
 
-unsigned long return_address(int depth);
-
-#define ftrace_return_address(n) return_address(n)
+#define ftrace_return_address(n) __builtin_return_address(n)
 
 void _mcount(void);
 void ftrace_caller(void);

arch/s390/kernel/dumpstack.c

@@ -87,30 +87,6 @@ void dump_trace(dump_trace_func_t func, void *data, struct task_struct *task,
 }
 EXPORT_SYMBOL_GPL(dump_trace);
 
-struct return_address_data {
-	unsigned long address;
-	int depth;
-};
-
-static int __return_address(void *data, unsigned long address, int reliable)
-{
-	struct return_address_data *rd = data;
-
-	if (rd->depth--)
-		return 0;
-	rd->address = address;
-	return 1;
-}
-
-unsigned long return_address(int depth)
-{
-	struct return_address_data rd = { .depth = depth + 2 };
-
-	dump_trace(__return_address, &rd, NULL, current_stack_pointer());
-	return rd.address;
-}
-EXPORT_SYMBOL_GPL(return_address);
-
 static int show_address(void *data, unsigned long address, int reliable)
 {
 	if (reliable)