fix dissect doc "ip" --> "clientip" (#38544)

Forward port of #38512.

Author: jakelandis

docs/reference/ingest/processors/dissect.asciidoc

@@ -170,7 +170,7 @@ Named skip key modifier example
 | *Pattern* | `%{clientip} %{?ident} %{?auth} [%{@timestamp}]`
 | *Input*   | 1.2.3.4 - - [30/Apr/1998:22:00:52 +0000]
 | *Result*  a|
-* ip = 1.2.3.4
+* clientip = 1.2.3.4
 * @timestamp = 30/Apr/1998:22:00:52 +0000
 |======