Fix validation failure issue for Knative service

[savitaashture]

Changes

PR fixes the issue reported here #1219 (comment)

Root Cause:
Its a regression issue which got introduced in 0.16.0 triggers while refactoring eventlistener code.

Previous fix : #995

/cc @dibyom @vaikas

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Release Notes

NONE

[tekton-robot]

@savitaashture: GitHub didn't allow me to request PR reviews from the following users: vaikas.

Note that only tektoncd members and repo collaborators can review this PR, and authors cannot review their own PRs.

In response to this:

Changes

PR fixes the issue reported here #1219 (comment)

Root Cause:
Its a regression issue which got introduced in 0.16.0 triggers while refactoring eventlistener code.

Previous fix : #995

/cc @dibyom @vaikas

Submitter Checklist

These are the criteria that every PR should meet, please check them off as you
review them:

• Includes tests (if functionality changed/added)
• Includes docs (if user facing)
• Commit messages follow commit message best practices
• Release notes block has been filled in or deleted (only if no user facing changes)

See the contribution guide for more details.

Release Notes

NONE

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[tekton-robot]

The following is the coverage report on the affected files.
Say /test pull-tekton-triggers-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/reconciler/eventlistener/eventlistener.go	70.0%	66.7%	-3.3
pkg/reconciler/eventlistener/resources/custom.go	93.8%	94.4%	0.6

[tekton-robot]

The following is the coverage report on the affected files.
Say /test pull-tekton-triggers-go-coverage to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/reconciler/eventlistener/eventlistener.go	70.0%	68.2%	-1.8

[savitaashture]

@dibyom this is the patch fix for 0.16.1

[dibyom]

/lgtm

[tekton-robot]

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