of: Add missing exports of node name compare functions

Commit f42b0e18 ("of: add node name compare helper functions")
failed to add the module exports to of_node_name_eq() and
of_node_name_prefix(). Add them now.

Fixes: f42b0e18 ("of: add node name compare helper functions")
Signed-off-by: Rob Herring <robh@kernel.org>