Revert "ath9k: Parse DTIM period from mac80211"

This reverts commit 0ce3bcfc.

Event though with the above commit we obtain the configured DTIM period
from the AP rather than always hardcoding it to '1', this seems to cause
problems under the following scenarios:
* Preventing association with broken AP's
* Adds latency in roaming
So its better to always use the safe value of '1' for dtim period

Cc: Jouni Malinen <Jouni.Malinen@Atheros.com>
Signed-off-by: Mohammed Shafi Shajakhan <mshajakhan@atheros.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>