rockchip: i2c: move ACK comment where it applies

rockchip: i2c: move ACK comment where it applies

The I2C_CON_LASTACK is kind of a misnomer as setting it means sending a
NACK as last byte acknowledge when the controller is in receive mode. It
should therefore be used only when there's no more data to transfer
after this.

Move the comment in the proper if block.

Sync the comment with the Linux kernel's while at it so it's more
explicit.

Fixes: 5deaa530280f ("rockchip: i2c: fix >32 byte reads")
Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>
Reviewed-by: Heiko Schocher <hs@nabladev.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>