ath11k: debugfs: Fix spelling mistake "Opportunies" -> "Opportunities"

There is a spelling mistake in some debug text, fix this.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210212113627.212787-1-colin.king@canonical.com