ath6kl: fix reading of FW IE capabilities

For some strange reason I used ALIGN() to calculate index to the
buffer. That is totally bogus and wouldn't work when it tried to read
the second bit. Fix it by removing the ALIGN() altogether.

Also check that ie_len is not too short.

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