Fix failure in mjsunit/regress/regress-5213. When bailout happens,
the double registers are not properly loaded if exponent_type() is
INTEGER (this happens in optimized version of code only).

BUG=mjsunit/regress/regress-5213

Review-Url: https://codereview.chromium.org/2175633003
Cr-Commit-Position: refs/heads/master@{#38013}