Use proper type for counter

Author: lantiga

torch/csrc/generic/Tensor.cpp

@@ -26,7 +26,7 @@
 #define COPY_FROM_ARRAY(ELTYPE) \
 { \
  ELTYPE *data = (ELTYPE*)PyArray_DATA(array); \
- for (ptrdiff_t i=0; i<storage_size; i++) { \
+ for (size_t i=0; i<storage_size; i++) { \
  storage->data[i] = data[i]; \
  } \
 }