dtc: Revert unintentional submodule downgrade from commit 077dd742

Commit 077dd742 inadvertently downgraded the 'dtc' submodule,
undoing the increment added in commit 6e85fce0. Revert this,
returning the submodule state to where we should be.
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

dtc @ ec02b34c

-Subproject commit 65cc4d2748a2c2e6f27f1cf39e07a5dbabd80ebf
+Subproject commit ec02b34c05be04f249ffaaca4b666f5246877dea