rcu: Fix TINY_RCU #elif condition

rcu: Fix TINY_RCU #elif condition

Some compilers are happy with "#elif CONFIG_RCU_TINY", while
others strongly prefer "#elif defined(CONFIG_RCU_TINY)".  Change
to the latter to make more compilers happy.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: laijs@cn.fujitsu.com
Cc: dipankar@in.ibm.com
Cc: mathieu.desnoyers@polymtl.ca
Cc: josh@joshtriplett.org
Cc: dvhltc@us.ibm.com
Cc: niv@us.ibm.com
Cc: peterz@infradead.org
Cc: rostedt@goodmis.org
Cc: Valdis.Kletnieks@vt.edu
Cc: dhowells@redhat.com
LKML-Reference: <12565906642768-git-send-email->
Signed-off-by: Ingo Molnar <mingo@elte.hu>