fix signature for upload dialog in gb2

fixes CNVS-10606

test-plan
=======
- navigate to gradebook and upload a csv of scores
- verify that uploading works as expected
- navigate to gradebook and submit the upload dialog without a file
- verify that the error banner shows across the top

Change-Id: I384ca0cfd33612050b218a174a714f4bb350af69
Reviewed-on: https://gerrit.instructure.com/28835
QA-Review: Caleb Guanzon <cguanzon@instructure.com>
Reviewed-by: Simon Williams <simon@instructure.com>
Tested-by: Bryan Madsen <bryan@instructure.com>
Product-Review: Bryan Madsen <bryan@instructure.com>