Optimizing: Use dex pc 0 for pattern substitution-generated IGET.

In the read barrier configuration, HInstanceFieldGet needs
a slow-path with a runtime call with an associated stack map
and we assert that we have a valid dex pc for stack maps.
Fix the pattern substitution-generated HInstanceFieldGet to
use the valid, if bogus, dex pc 0.

Bug: 26854537
Bug: 12687968

Change-Id: I9f379ea530ce3f89af8db40169a6c41b525abbd7
1 file changed