i2c: sh_mobile: devm conversion, low hanging fruits

Convert the easy parts to devm. irqs will be converted in a seperate
patch to keep diffs readable.

Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>