RFR: fixed libffmpeg samples for "$slice" removal in struct field accessors

[Athijegannathan Sundararajan]

fixed libffmpeg samples for "$slice" removal in struct field accessors

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Commit messages:
 - fixed libffmpeg samples for "$slice" removal in struct field accessors

Changes: https://git.openjdk.org/jextract/pull/184/files
 Webrev: https://webrevs.openjdk.org/?repo=jextract&pr=184&range=00
  Stats: 5 lines in 1 file changed: 0 ins; 0 del; 5 mod
  Patch: https://git.openjdk.org/jextract/pull/184.diff
  Fetch: git fetch https://git.openjdk.org/jextract.git pull/184/head:pull/184

PR: https://git.openjdk.org/jextract/pull/184