scripts/dtc: Update to upstream version v1.4.5-6-gc1e55a5513e9

Pickup the fix for handling unresolved phandles in overlays.

This adds the following commits from upstream:

c1e55a5513e9 checks: fix handling of unresolved phandles for dts plugins
f8872e29ce06 tests: Avoid 64-bit arithmetic in assembler
48c91c08bcfa libfdt: add stringlist functions to linker script

Signed-off-by: Rob Herring <robh@kernel.org>