hw_random: Remove BKL from core

hw_random core is completely serialized with rng_mutex. No need for
the cycle_kernel_lock() magic.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
LKML-Reference: <20091010153349.844488872@linutronix.de>
Cc: Herbert Xu <herbert@gondor.apana.org.au>