Fix bit math

Summary:
Formerly `static_cast<StreamId>(bits)` and `static_cast<DeviceIndex>(bits)` were and-ed against `ull` types resulting in an integer promotion which later raised a warning in downcasting passes to  `Stream` and `Device`.

Moving the `&` operation inside the cast results in two `uint64_t` being operated on and then cast to the correct type, eliminating the warning.

Test Plan: Standard pre-commit test rig.

Differential Revision: D24481292

fbshipit-source-id: 16ba68690e58ce8b710bb082542c1a5451548742

c10/core/Stream.h

@@ -124,11 +124,11 @@ class Stream final {
   }
 
   static Stream unpack(uint64_t bits) {
-    auto stream_id = static_cast<StreamId>(bits) & 0xFFFFFFFFull;
+    const auto stream_id = static_cast<StreamId>(bits & 0xFFFFFFFFull);
     bits >>= 32;
-    auto device_index = static_cast<DeviceIndex>(bits) & 0xFFFFull;
+    const auto device_index = static_cast<DeviceIndex>(bits & 0xFFFFull);
     bits >>= 16;
-    auto device_type = static_cast<DeviceType>(bits);
+    const auto device_type = static_cast<DeviceType>(bits);
     TORCH_CHECK(isValidDeviceType(device_type));
     // Unfortunately, we can't check if the StreamId is valid here; it
     // will be checked upon first use.