random: always update the entropy pool under the spinlock
random: always update the entropy pool under the spinlock

Instead of using lockless techniques introduced in commit
902c098a3663, use spin_trylock to try to grab entropy pool's lock.  If
we can't get the lock, then just try again on the next interrupt.

Based on discussions with George Spelvin.

Signed-off-by: Theodore Ts'o <4ed386e0495d3e109932df055831d9ec2f824927@mit.edu>
Cc: George Spelvin <ba324ca7b1c77fc20bb970d5aff6eea9377918a5@horizon.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs