dtc: fix for_each_*() to skip first object if deleted

The previous definition of for_each_*() would always include the very
first object within the list, irrespective of whether it was marked
deleted, since the deleted flag was not checked on the first object,
but only on any "next" object.

Fix for_each_*() to check the deleted flag in the loop body every
iteration to correct this.

(upstream dtc commit 1762ab42ef77db7ab2776d0d6cba3515150f518a)

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Rob Herring <rob.herring@calxeda.com>