i2c: Remove usage of orphaned symbol OF_I2C

The symbol is an orphan, don't depend on it anymore.

Signed-off-by: Richard Weinberger <richard@nod.at>
[wsa: enhanced commit message]
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Fixes: 687b81d0 (i2c: move OF helpers into the core)
Cc: stable@kernel.org