[ganesh] Fix maxLCDOffset calculation

The CL https://skia-review.git.corp.google.com/c/skia/+/1251156 had a
logic mistake in the Ganesh implementation. Graphite's localAARadius
helper automatically computes 1/minScale (with awareness for
perspective). We need the inverse of the scale factor since we are going
from device space to local space; we switch to the minScale instead of
the maxScale singular value because it's used in the denominator.

Bug: 519229200
Change-Id: Iaf98ef20289c169edf569b846eda120e0bf3e4e7
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/1253436
Reviewed-by: Nicolette Prevost <nicolettep@google.com>
Commit-Queue: Michael Ludwig <michaelludwig@google.com>