i2c: microchip: fix ack sending logic

"Master receive mode" was not correctly sending ACKs/NACKs in the
interrupt handler. Bring the handling of M_SLAR_ACK, M_RX_DATA_ACKED &
M_RX_DATA_NACKED in line with the Linux driver.

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