hwrng: nomadik - Use devm_*() functions

Use devm_*() functions to make cleanup paths simpler.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>