s390/ftrace: remove incorrect __va usage

The address of ftrace_graph_caller is already virtual.
Using __va() to translate the address is wrong.
Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

arch/s390/kernel/ftrace.c

@@ -341,13 +341,13 @@ NOKPROBE_SYMBOL(prepare_ftrace_return);
  */
 int ftrace_enable_ftrace_graph_caller(void)
 {
-	brcl_disable(__va(ftrace_graph_caller));
+	brcl_disable(ftrace_graph_caller);
 	return 0;
 }
 
 int ftrace_disable_ftrace_graph_caller(void)
 {
-	brcl_enable(__va(ftrace_graph_caller));
+	brcl_enable(ftrace_graph_caller);
 	return 0;
 }