InitSshd: Use correct flag to set empty passphrase
InitSshd: Use correct flag to set empty passphrase

From https://www.ssh.com/ssh/keygen/:
  -N "New" Provides a new passphrase for the key.
  -P "Passphrase" Provides the (old) passphrase when reading a key.

PiperOrigin-RevId: 210948400
Change-Id: Iba3a674f81686987fef60f0fd5a5f42aa5b9dd86

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