ath6kl: Remove redundant key_index check.

Less-than-zero comparison of an unsigned value is never true.

kvalo: remove WMI_MIN_KEY_INDEX altogether, it's useless

Signed-off-by: Vivek Natarajan <nataraja@qca.qualcomm.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>