design/6977-overlapping-interfaces.md: fix naming inconsistency
design/6977-overlapping-interfaces.md: fix naming inconsistency

s/hardware/device/ and while at it, use `device` and `wallet`
in the same order consistently.

Change-Id: I9b41448d99425ff9f96a32c3d62a4fdaaaa24bbb
Reviewed-on: https://go-review.googlesource.com/c/proposal/+/201458
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

golang/proposal,golang/proposal