hwrng: omap3-rom - Remove obsoleted functions

Remove omap3_rom_rng_data_present method as it was returning 1 always.
Use .read callback instead of .data_read callback. This avoids use of
obsolete callbacks.

This patch is not tested with hardware as I don't have access to it.

Signed-off-by: PrasannaKumar Muralidharan <prasannatsmkumar@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>