i2c: hisi: Add clearing tx aempty interrupt operation

The driver receives the tx fifo almost empty(aempty) interrupt and
reads the tx_aempty_int_mstat to start a round of data transfer.
The operation of clearing the TX aempty interrupt after completing
a write cycle is added to ensure that the FIFO is truly at almost
empty status when an aempty interrupt is received.
The threshold for fifo almost empty interrupt is defined as 1.

Signed-off-by: Devyn Liu <liudingyuan@huawei.com>
Reviewed-by: Yicong Yang <yangyicong@hisilicon.com>
Reviewed-by: Andi Shyti <andi.shyti@kernel.org>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>