mesh: shell: Fix AppKey Add command handler
mesh: shell: Fix AppKey Add command handler

The command handler already has support for decoding from hex, however
it was not using the decoded value when calling the client API.

X-Original-Commit: 1fa3239e79d261943e7bd783b5e0437f1f7dc072

apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble,apache/mynewt-nimble