use .Values.serviceAccount.name for rolebinding

[fivesheep]

Signed-off-by: Xiayang Wu xwu@rippling.com

Provide a description of what has been changed

For #189
The rolebindings did not use the serviceAccount.name, and the helmchart will only work when setting serviceAccount.name same as operator.name, which is not always the case

Checklist

• Commits are signed with Developer Certificate of Origin (DCO - learn more)
• A PR is opened to update KEDA core (repo) (if applicable, ie. when deployment manifests are modified)
• README is updated with new configuration values (if applicable)

Fixes #

[tomkerkhove]

Makes sense, thank you!