Instead of always loading the instance from the frame, try to use the
cached instance register instead.
This is totally not performance critical since we do a C call afterwards
anyway, but it's just as easy to use the cached instance than loading it
fresh from the stack.

R=thibaudm@chromium.org

Change-Id: Ia815e9e6f8ab2efc665b2e3aefcdc7b4aa95739f
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3427461Reviewed-by: Thibaud Michaud <thibaudm@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78929}