Fix c5c50e18

After the change from the title landed, around 700 tests started
failing on MIPS and MIPS64. The reason for the failure was a typo
in Generate_JSBuiltinsConstructStubHelper in builtin-mips.cc
and builtin-mips64.cc.

Bug: 
Change-Id: Id95a87773d6ab1d4a65c3c7a306629046a44fa7d
Reviewed-on: https://chromium-review.googlesource.com/771652Reviewed-by: Miran Karić <Miran.Karic@imgtec.com>
Commit-Queue: Ivica Bogosavljevic <ivica.bogosavljevic@mips.com>
Cr-Commit-Position: refs/heads/master@{#49382}