Fix 8238562b

Requirement that the address is stored kJavaScriptCallCodeStartRegister
caused failures on MIPSR6, because of R6 optimization which doesn't load
the address in kJavaScriptCallCodeStartRegister.

Change-Id: If05d8bfe8601288b10fc65cca77664fe9638bbe9
Reviewed-on: https://chromium-review.googlesource.com/910851Reviewed-by: Miran Karić <miran.karic@mips.com>
Commit-Queue: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
Cr-Commit-Position: refs/heads/master@{#51212}