s390/ptrace: simplify enable/disable single step

The user_enable_single_step() and user_disable_sindle_step() functions
are always called on the inferior, never for the currently active
process. Remove the unnecessary check for the current process and
the update_cr_regs() call from the enable/disable functions.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/ptrace.c

@@ -107,15 +107,11 @@ void update_cr_regs(struct task_struct *task)
 void user_enable_single_step(struct task_struct *task)
 {
 	set_tsk_thread_flag(task, TIF_SINGLE_STEP);
-	if (task == current)
-		update_cr_regs(task);
 }
 
 void user_disable_single_step(struct task_struct *task)
 {
 	clear_tsk_thread_flag(task, TIF_SINGLE_STEP);
-	if (task == current)
-		update_cr_regs(task);
 }
 
 /*