i2c: nomadik: replace jiffies by ktime for FIFO flushing timeout

The FIFO flush function uses a jiffies amount to detect timeouts as the
flushing is async. Replace with ktime to get more accurate precision
and support short timeouts.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Andi Shyti <andi.shyti@kernel.org>
Signed-off-by: Théo Lebrun <theo.lebrun@bootlin.com>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>