ParseEncryptedRawPrivateKey should return *ed25519.PrivateKey

[jduepmeier]

To be compatible with the crypto/ssh the ParseEncryptedRawPrivateKey should return a pointer to ed25519.PrivateKey.
I think this can be fixed on this line:

sshkeys/parse.go

Line 210 in 82451a8

pk := ed25519.PrivateKey(make([]byte, ed25519.PrivateKeySize))