i2c: sh_mobile: simplify sending address for RX

pd->pos won't be smaller than -1, so we can simplify the logic.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>