s390: always inline current_stack_pointer()

This function must be inlined since any caller expects the current
stack pointer; which wouldn't be true if the function isn't inlined.
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

arch/s390/include/asm/processor.h

@@ -206,7 +206,7 @@ unsigned long get_wchan(struct task_struct *p);
 /* Has task runtime instrumentation enabled ? */
 #define is_ri_task(tsk) (!!(tsk)->thread.ri_cb)
 
-static inline unsigned long current_stack_pointer(void)
+static __always_inline unsigned long current_stack_pointer(void)
 {
 	unsigned long sp;