i2c: imx: don't change platform device id_entry directly

The id_entry field should be changed by platform driver core,
driver should prevent changing it derectly. Use local variable
to save and extract platform_device_id info of the dts devices
instead.

Signed-off-by: Jingchang Lu <b35083@freescale.com>
Reviewed-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>