usb: misc: usb3503: Set platform data

Driver supports two paths of device instantiation: as platform and i2c
device. In the platform path it lacks of storing the driver specific
structure as drvdata.

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>