ath6kl: Remove auth type fall back in auto authentication mode

Target already tries with different authentication mechanism
when authentication type is configured to NL80211_AUTHTYPE_AUTOMATIC.
Remove this piece of code from driver. Having this code in driver
even affects auto + WEP authentication in some cases.

Signed-off-by: Vasanthakumar Thiagarajan <vthiagar@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>