um: Remove BKL from random

cycle_kernel_lock() was added during the big BKL pushdown. It should
ensure the serializiation against driver init code. In this case there
is nothing to serialize. Remove it.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
LKML-Reference: <20091010153349.641118498@linutronix.de>
Cc: Jeff Dike <jdike@addtoit.com>