🐛 Fix undefined local variable `iiif_print`

[kirkkwang]

Story

There was a change in this version of IIIF Print that needed an update to routes.rb.

Ref:

• https://github.com/scientist-softserv/utk-hyku/issues/614
• https://github.com/scientist-softserv/iiif_print/pull/302

Expected Behavior Before Changes

Viewing the file set show page as an admin would result in a crash.

Expected Behavior After Changes

Admins can view the file set show page without crashing.

Screenshots / Video