ath6kl: Remove bogus non-NULL pointer check

In ath6kl_cfg80211_add_key(), params is checked for non-NULL
but this pointer has been deferenced many times before this check. This
gives the following smatch warning. add_key() can never carry NULL as
params, remove this bogus check.

ath6kl_cfg80211_add_key(86) warn: variable dereferenced before check 'params'

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