mce: convert to rcu_dereference_index_check()

The mce processing applies rcu_dereference_check() to integers used as
array indices.  This patch therefore moves mce to the new RCU API
rcu_dereference_index_check() that avoids the sparse processing that
would otherwise result in compiler errors.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>