More conditional imports

nabu/cuda/convolution.py

 import numpy as np
 from os.path import dirname
 from silx.image.utils import gaussian_kernel
-from ..utils import updiv, get_cuda_srcfile, __has_pycuda__
+from ..utils import updiv, get_cuda_srcfile
+from ..cuda.utils import __has_pycuda__
 from ..misc.utils import ConvolutionInfos
 from .processing import CudaProcessing