um: get_safe_registers() should be done in flush_thread(), not start_thread()

... or we'll end up buggering the results of ELF_PLAT_INIT()
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

arch/um/kernel/exec.c

@@ -32,13 +32,14 @@ void flush_thread(void)
 		       "err = %d\n", ret);
 		force_sig(SIGKILL, current);
 	}
+	get_safe_registers(current_pt_regs()->regs.gp,
+			   current_pt_regs()->regs.fp);
 
 	__switch_mm(&current->mm->context.id);
 }
 
 void start_thread(struct pt_regs *regs, unsigned long eip, unsigned long esp)
 {
-	get_safe_registers(regs->regs.gp, regs->regs.fp);
 	PT_REGS_IP(regs) = eip;
 	PT_REGS_SP(regs) = esp;
 	current->ptrace &= ~PT_DTRACE;