lockdep: Actually _dec_ in debug_atomic_dec

Fix a silly copy-paste mistake that was making debug_atomic_dec use
this_cpu_inc instead of this_cpu_dec.

Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>

diff --cc kernel/lockdep_internals.h
Simple merge