i2c: sh_i2c.c: check error in i2c_read and i2c_write

Before this patch, i2c_{read,write} always returned 0.
Check TACK in i2c_raw_{read,write} so that i2c_{read,write} return non-zero when error.

Acked-by: Nobuhiro Iwamatsu <nobuhiro.iwamatsu.yj@renesas.com>
Signed-off-by: Tetsuyuki Kobayashi <koba@kmckk.co.jp>