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.

Signed-off-by: Sergey Matyukevich <sergey.matyukevich@synopsys.com>

Author: Sergey Matyukevich

arch/arc/kernel/entry.S

@@ -175,6 +175,7 @@ tracesys_exit:
 	STR  r0, sp, PT_r0
 
 	; POST syscall trace hook
+	MOVR r0, sp				; pt_regs
 	bl  @syscall_trace_exit
 
 	; don't call ret_from_system_call as it saves r0, already done above