commit 3c96a2 (ipc: Make the ipc code -rt aware) introduced a
imbalance of preempt_disable_rt vs. preempt_enable_nort. That results
in preempt count leak.

Make it symetric.
Reported-by: Joerg Abraham <Joerg.Abraham@alcatel-lucent.de>
Signed-off-by: John Kacur <jkacur@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>