Update blendmode benchmark to allow less than 1000 iterations.

On Mali 400 devices, 1000 iterations is way too many, causing this
benchmark to take five seconds per variation:
http://screen/5AdKPZynP7myjfR

This change should help lighten the load on the tree for older devices.

Change-Id: I3f719093c3f7fdbc81ab41c29ce6d93f36360b7b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/388444
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
1 file changed