Fix a bug in ClassTableGet code generation for IMTs.

Introduced by:
  https://android-review.googlesource.com/#/c/244980/

test:566-polymorphic-inling for fixing x86 crash. Also
fixes a performance regression.
bug:29188168

(cherry picked from commit ff484b95)

Change-Id: Iae5a63cb24017222c3fefda695a0a39673719f51