Fix the NameError failing every PR validation

[tangosdev]

Every PR validation is currently dying before it produces a report. The gate surfaces it as Worker error -- validate_merge produced no report, which reads like validator infrastructure, but it is a one-word repo bug:

File "/home/validator/clone/tools/validate_merge.py", line 98, in <setcomp>
    if asm_policy.has_draft_banner(git_text(rev, path))}
NameError: name 'asm_policy' is not defined

tools/validate_merge.py:29 imports the module as import asm_policy as AP, so the bare name asm_policy does not exist. #1367 added the function_snapshot draft-banner filter using the un-aliased spelling. It is the only such use in the file; chaos_db_ci and rombuild_check are both referenced through their aliases correctly.

Why #1367 went green: the crash is in a code path only the validator worker runs, so submit and ratchet had nothing to say about it, and the byte gate that would have caught it is the very thing that broke.

Verified both directions on this tree rather than by inspection:

• before: function_snapshot('HEAD') raises NameError: name 'asm_policy' is not defined
• after: returns a dict, 3 entries

Found while chasing #1369, whose validation went from mwccarm failed to Worker error the moment I merged current main into its branch. #1370 is green only because it was validated before #1367 reached its tree.

[tangos-validator]

✅ PR validation — Passed

noverify: no source/build-data changes in this PR

_{Each changed src/*.c|*.cpp is compiled and its relocated bytes compared to the binary data on a private build box. Passing requires every changed file to reproduce the ROM byte-for-byte with correct relocation targets — this catches WRONG-DEST relocations and non-reproducing near-misses that ledger-scoped linkcheck skips.}