Fix warnings by Coverity Scan

Use move instead of copy.

Src/Base/AMReX_BoxArray.cpp

@@ -555,9 +555,10 @@ BoxArray::maxSize (const IntVect& block_size)
  blst.maxSize(block_size);
  const int N = static_cast<int>(blst.size());
  if (size() != N) { // If size doesn't change, do nothing.
- auto bak = m_simplified_list;
+ std::shared_ptr<BoxList> bak;
+ bak.swap(m_simplified_list);
  define(std::move(blst));
- m_simplified_list = bak;
+ m_simplified_list = std::move(bak);
  }
  return *this;
 }
@@ -569,12 +570,12 @@ BoxArray::minmaxSize (const IntVect& min_size, const IntVect& max_size)
  (max_size/min_size)*min_size == max_size);
  std::shared_ptr<BoxList> bak;
  if (m_bat.is_simple() && crseRatio() == IntVect::TheUnitVector()) {
- bak = m_simplified_list;
+ bak.swap(m_simplified_list);
  }
  this->coarsen(min_size);
  this->maxSize(max_size/min_size);
  this->refine(min_size);
- m_simplified_list = bak;
+ m_simplified_list = std::move(bak);
  return *this;
 }