syscall: do not overflow key memory in GetQueuedCompletionStatus

The third argument to GetQueuedCompletionStatus is a pointer to a
uintptr, not a uint32. Users of this functions have therefore been
corrupting their memory every time they used it. Either that memory
corruption was silent (dangerous), or their programs didn't work so they
chose a different API to use.

Fixes #44538.

RELNOTES=yes

Change-Id: Idf48d4c712d13da29791e9a460159255f963105b
Reviewed-on: https://go-review.googlesource.com/c/go/+/295371


Trust: Jason A. Donenfeld <Jason@zx2c4.com>
Run-TryBot: Jason A. Donenfeld <Jason@zx2c4.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>