target/xtensa: linux-user: rewind pc for restarted syscall

In case of syscall restart request set pc back to the syscall
instruction.

Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

linux-user/main.c

@@ -4006,6 +4006,9 @@ void cpu_loop(CPUXtensaState *env)
                     break;
 
                 case -TARGET_ERESTARTSYS:
+                    env->pc -= 3;
+                    break;
+
                 case -TARGET_QEMU_ESIGRETURN:
                     break;
                 }