Update device_auth.md

[YLSDev]

Device Auth ignores client now

[MixV2]

Are you able to confirm this again?

I get errors.com.epicgames.account.invalid_account_credentials when trying to authenticate with a different client from the one that I generated device auth credentials for.

[YLSDev]

Yup I just generated a device auth on ios client and used it on android client

[Jaren8r]

I just tried doing that exact same thing, and I am getting the same error as mix.