I2C: OMAP: remove unneccesary use of pdev

A pointer to the struct device associated with the i2c device is
already kept in the struct omap_i2c_dev, so use omap_i2c_device to
find the pointer to struct device.

Reviewed-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>