Fixed ucf video download url

[aws-caijune]

Description:

*Issue https://t.corp.amazon.com/V1503192060

• Link to RTD for my changes: https://github.com/aws-neuron/aws-neuron-samples/tree/caijune-fix-perceiver-input

• Submitter Checklist [pending update]

  • Tested on : release versionset neuron-ops/release-2.20@6247153458, trn1+inf2
  • output from KaenaGithubTests

=============== CPython38-samples_inference_release_prs SUCCESS ================
BrazilPython timings:
get package info                                                      14.00s
brazil-path:package-vars                                              3.00s
samples_inference_release_prs:CPython38                               2323.65s
samples_inference_release_prs:total                                   2323.65s
BUILD SUCCEEDED

• Reviewer Checklist
  * I've verified the changes render correctly on RTD (link above)
  * I've ensured the submitter completed the form
  * (If appropriate) I've verified the metrics.json file provided by the submitter