ath6kl: add ath6kl_bmi_write_hi32()

We have a lot of 32 bit writes to the host interest area and the code
doing that is ugly. Clean that up by adding ath6kl_bmi_write_hi32().

This also fixes few checkpatch warnings.

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