ath6kl: add ath6kl_bmi_read_hi32()

There are few 32 bit reads from the host interest area. Add
ath6kl_bmi_read_hi32() to make it easier to do that. As code is cleaner
this also fixes few checkpatch warnings.

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