ath11k: fix spelling mistake "moniter" -> "monitor"

There is a spelling mistake in an ath11k_warn warning 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/20200819074729.48591-1-colin.king@canonical.com