i2c: microchip: fix erroneous late ack send

A late ack is currently being sent at the end of a transfer due to
incorrect logic in mchp_corei2c_empty_rx(). Currently the Assert Ack
bit is being written to the controller's control reg after the last
byte has been received, causing it to sent another byte with the ack.
Instead, the AA flag should be written to the control register when
the penultimate byte is read so it is sent out for the last byte.

Reported-by: Andreas Buerkler <andreas.buerkler@enclustra.com>
Fixes: 0dc0d1e0 ("i2c: Add Microchip PolarFire SoC I2C driver")
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>
Reviewed-by: Padmarao Begari <padmarao.begari@microchip.com>
Reviewed-by: Heiko Schocher <hs@denx.de>

Removed Tag by hs: Fixes: 0190d48488 ("i2c: microchip: fix ack sending logic")