cmd/compile: correct capitalization in recordFlags parameter

Tool refactoring smallStacks into smallFrames helpfully
"corrected" the capitalization in a string, this undoes
the help.

This is necessary to ensure correct (re)building when the
flag is used to research stack-marking GC latency bugs.

Updates #27732.

Change-Id: Ib7c8d4a36c9e4f9612559be68bd481f9d9cc69f1
Reviewed-on: https://go-review.googlesource.com/c/go/+/180958


Run-TryBot: David Chase <drchase@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>