i2c: uniphier-f: fill TX-FIFO only in IRQ handler for repeated START

- For a repeated START condition, this controller starts data transfer
   immediately after the slave address is written to the TX-FIFO.

 - Once the TX-FIFO empty interrupt is asserted, the controller makes
   a pause even if additional data are written to the TX-FIFO.

Given those circumstances, the data after a repeated START may not be
transferred if the interrupt is asserted while the TX-FIFO is being
filled up. A more reliable way is to append TX data only in the
interrupt handler.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>