pw_rpc: Don't use PW_CHECK in a constexpr function

PW_CHECK may expand to code that cannot be used in a constexpr function.
PW_ASSERT will be constexpr-friendly, but that is not available yet.

Change-Id: I5e5cf2af0f49c7de4530f4fb1938585b7f4b69f7
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/18283
Reviewed-by: Keir Mierle <keir@google.com>
Commit-Queue: Wyatt Hepler <hepler@google.com>
diff --git a/pw_rpc/public/pw_rpc/channel.h b/pw_rpc/public/pw_rpc/channel.h
index 1b95082..6d14357 100644
--- a/pw_rpc/public/pw_rpc/channel.h
+++ b/pw_rpc/public/pw_rpc/channel.h
@@ -63,11 +63,13 @@
  protected:
   constexpr Channel(uint32_t id, ChannelOutput* output)
       : id_(id), output_(output) {
-    PW_CHECK_UINT_NE(id, kUnassignedChannelId);
+    // TODO(pwbug/246): Use PW_ASSERT when that is available.
+    // PW_ASSERT(id != kUnassignedChannelId);
   }
 
   ChannelOutput& output() const {
-    PW_CHECK_NOTNULL(output_);
+    // TODO(pwbug/246): Use PW_ASSERT when that is available.
+    // PW_ASSERT(output_ != nullptr);
     return *output_;
   }