tools/memory-model: Make read_foo_diagnostic() more clearly diagnostic
The current definition of read_foo_diagnostic() in the "Lock Protection
With Lockless Diagnostic Access" section returns a value, which could
be use for any purpose. This could mislead people into incorrectly
using data_race() in cases where READ_ONCE() is required. This commit
therefore makes read_foo_diagnostic() simply print the value read.
Reported-by: Manfred Spraul <manfred@colorfullife.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>