driver: i2c: i2c_dw: clear block mode on init

Depending on the IP's `IC_TX_CMD_BLOCK_DEFAULT` parameter, we
might have to clear the `TX_CMD_BLOCK` bit on init so that
Controller mode works.

Signed-off-by: Yong Cong Sin <ycsin@meta.com>
Signed-off-by: Yong Cong Sin <yongcong.sin@gmail.com>