hwrng: imx-rngc - don't init of_device_id's data

We have no device-specific data for fsl,imx25-rngb. There's no need to
set .data = NULL, this is the default.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>