pw_rpc: Update docs to reference call_id instead of client ID

"call_id" was incorrectly described as "client ID".

Change-Id: Ia021e8e9a06388e349268758e54eb6b10001cd04
Reviewed-on: https://pigweed-review.googlesource.com/c/pigweed/pigweed/+/80841
Reviewed-by: Alexei Frolov <frolv@google.com>
Commit-Queue: Erik Gilling <konkers@google.com>
diff --git a/pw_rpc/docs.rst b/pw_rpc/docs.rst
index b8af1a0..6869470 100644
--- a/pw_rpc/docs.rst
+++ b/pw_rpc/docs.rst
@@ -594,7 +594,7 @@
 |                   |                                     |
 +-------------------+-------------------------------------+
 
-All server packets contain the same client ID that was set in the initial
+All server packets contain the same ``call_id`` that was set in the initial
 request made by the client, if any.
 
 **Server errors**