COMP: WindowedSincInterpolate OffsetTable return type [VS2017 fix]

Fixes compile error on Visual Studio 2017. The full error message is:

M:\Dashboard\ITK\Modules\Core\ImageFunction\include\itkWindowedSincInterpolateImageFunction.h(346): error C2397: conversion from 'TReturnType' to 'const unsigned int' requires a narrowing conversion [M:\Dashboard\ITK-build\Modules\Core\Common\test\ITKCommon1TestDriver.vcxproj]

M:\Dashboard\ITK\Modules\Core\Common\test\itkPhasedArray3DSpecialCoordinatesImageTest.cxx(96): note: see reference to class template instantiation 'itk::WindowedSincInterpolateImageFunction<Image,3,itk::Function::HammingWindowFunction<3,double,double>,itk::ZeroFluxNeumannBoundaryCondition<TInputImage,TInputImage>,double>' being compiled

Modules/Core/ImageFunction/include/itkWindowedSincInterpolateImageFunction.h

@@ -343,7 +343,7 @@ class ITK_TEMPLATE_EXPORT WindowedSincInterpolateImageFunction : public Interpol
   TWindowFunction m_WindowFunction;
 
   /** Size of the offset table */
-  static constexpr unsigned int m_OffsetTableSize{ Math::UnsignedPower(m_WindowSize, ImageDimension) };
+  static constexpr unsigned int m_OffsetTableSize = Math::UnsignedPower(m_WindowSize, ImageDimension);
 
   /** The offset array, used to keep a list of relevant
    * offsets in the neihborhoodIterator */