Correct invalid or missing return types (#14587)

Found some invalid return statements when compiling cudf with a newer gcc.

Authors:
  - Robert Maynard (https://github.com/robertmaynard)

Approvers:
  - David Wendt (https://github.com/davidwendt)
  - Shruti Shivakumar (https://github.com/shrshi)

URL: #14587

cpp/src/io/parquet/page_delta_decode.cu

@@ -213,7 +213,7 @@ struct delta_byte_array_decoder {
     using cudf::detail::warp_size;
     __shared__ __align__(8) uint8_t* so_ptr;
 
-    if (start_idx >= suffixes.value_count) { return; }
+    if (start_idx >= suffixes.value_count) { return 0; }
     auto end_idx = start_idx + min(suffixes.values_per_mb, num_values);
     end_idx      = min(end_idx, static_cast<uint32_t>(suffixes.value_count));
 

cpp/src/text/jaccard.cu

@@ -113,7 +113,7 @@ struct sorted_intersect_fn {
   cudf::size_type* d_results;
 
   // warp per row
-  __device__ float operator()(cudf::size_type idx) const
+  __device__ void operator()(cudf::size_type idx) const
   {
     using warp_reduce = cub::WarpReduce<cudf::size_type>;
     __shared__ typename warp_reduce::TempStorage temp_storage;