hwrng: omap - Use pm_runtime_resume_and_get() to replace open coding

use pm_runtime_resume_and_get() to replace pm_runtime_get_sync and
pm_runtime_put_noidle. this change is just to simplify the code, no
actual functional changes.

Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>