Gate PrivBeginPrefix/PrivSuffix; init typeSz in ssh.c

[gojimmypi]

The PrivBeginPrefix and PrivSuffix are only used in wolfSSH_ReadKey_file() which is gated with:

#if !defined(NO_FILESYSTEM) && !defined(WOLFSSH_USER_FILESYSTEM)

... thus otherwise there's a compiler warning about them not being used on a no-filesystem target.

There's also a typeSz = 0 initialization that was failing as the Espressif compiler was complaining it was not initialized.

• Edit: see Espressif fixes: MISC_WARNING not expanded, vars not initialized, not used #633