use selected device instead of always cuda for UniPC sampler

import torch

from .uni_pc import NoiseScheduleVP, model_wrapper, UniPC

from modules import shared

from modules import shared, devices

class UniPCSampler(object):

    def __init__(self, model, **kwargs):

    def register_buffer(self, name, attr):

        if type(attr) == torch.Tensor:

            if attr.device != torch.device("cuda"):

                attr = attr.to(torch.device("cuda"))

            if attr.device != devices.device:

                attr = attr.to(devices.device)

        setattr(self, name, attr)

    def set_hooks(self, before_sample, after_sample, after_update):