ARC: entry: fix syscall_trace_exit argument

Function syscall_trace_exit expects pointer to pt_regs. However
r0 is also used to keep syscall return value. Restore pointer
to pt_regs before calling syscall_trace_exit.

Cc: <stable@vger.kernel.org>
Signed-off-by: Sergey Matyukevich <sergey.matyukevich@synopsys.com>
Signed-off-by: Vineet Gupta <vgupta@kernel.org>

Author: Sergey Matyukevich

arch/arc/kernel/entry.S

@@ -196,6 +196,7 @@ tracesys_exit:
 	st  r0, [sp, PT_r0]     ; sys call return value in pt_regs
 
 	;POST Sys Call Ptrace Hook
+	mov r0, sp		; pt_regs needed
 	bl  @syscall_trace_exit
 	b   ret_from_exception ; NOT ret_from_system_call at is saves r0 which
 	; we'd done before calling post hook above