[skcapture] Correct setSurfaceBase call to set the base drawing canvas

Change-Id: Id6befa80868489e331f0017326674b02c267ee30
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/1205856
Commit-Queue: Jorge Betancourt <jmbetancourt@google.com>
Reviewed-by: Greg Daniel <egdaniel@google.com>
Commit-Queue: Greg Daniel <egdaniel@google.com>
Auto-Submit: Jorge Betancourt <jmbetancourt@google.com>