checkpatch: Fix false DT_SPLIT_BINDING_PATCH warnings
Patches which both remove and add/modify DT binding files are
incorrectly flagged as needing to split the patch. The issue is the
check sees "dev/null" as one of the files in the patch which is not a DT
binding file. Add "dev/null" to the skipped files.
Link: https://patch.msgid.link/20260121212715.144495-1-robh@kernel.org
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>