ath6kl: fix spelling mistake "initilisation" -> "initialization"

There is a spelling mistake in an ath6kl_err error message. Fix it.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200806121958.60700-1-colin.king@canonical.com