hwrng: geode - Migrate to managed API

Use devm_ioremap and devm_hwrng_register instead of ioremap and
hwrng_register. This removes error handling code. Also moved code around
by removing goto statements. This improves code readability.

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