wireguard: noise: do not assign initiation time in if condition

Fixes an error condition reported by checkpatch.pl which caused by
assigning a variable in an if condition in wg_noise_handshake_consume_
initiation().

Signed-off-by: Frank Werner-Krippendorf <mail@hb9fxq.ch>
Signed-off-by: Jason A. Donenfeld <Jason@zx2c4.com>
Signed-off-by: David S. Miller <davem@davemloft.net>