documents to use unsigned offset types in scan's dispatch (#3111)

Author: elstehle

cub/cub/device/dispatch/dispatch_scan.cuh

@@ -143,7 +143,7 @@ DeviceCompactInitKernel(ScanTileStateT tile_state, int num_tiles, NumSelectedIte
  *   (cub::NullType for inclusive scans)
  *
  * @tparam OffsetT
- *   Signed integer type for global offsets
+ *   Unsigned integer type for global offsets
  *
  * @paramInput d_in
  *   data
@@ -223,7 +223,7 @@ __launch_bounds__(int(ChainedPolicyT::ActivePolicy::ScanPolicyT::BLOCK_THREADS))
  *   The init_value element type for ScanOpT (cub::NullType for inclusive scans)
  *
  * @tparam OffsetT
- *   Signed integer type for global offsets
+ *   Unsigned integer type for global offsets
  *
  * @tparam ForceInclusive
  *   Boolean flag to force InclusiveScan invocation when true.

cub/cub/device/dispatch/dispatch_scan_by_key.cuh

@@ -92,7 +92,7 @@ CUB_NAMESPACE_BEGIN
  *   The init_value element for ScanOpT type (cub::NullType for inclusive scan)
  *
  * @tparam OffsetT
- *   Signed integer type for global offsets
+ *   Unsigned integer type for global offsets
  *
  * @param d_keys_in
  *   Input keys data
@@ -217,7 +217,7 @@ CUB_DETAIL_KERNEL_ATTRIBUTES void DeviceScanByKeyInitKernel(
  *   The init_value element for ScanOpT type (cub::NullType for inclusive scan)
  *
  * @tparam OffsetT
- *   Signed integer type for global offsets
+ *   Unsigned integer type for global offsets
  *
  */
 template <