fixed doubleregister name in VisitFloat64Ieee754Binop and VisitFloat64Ieee754Unop

R=joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com, mbrandy@us.ibm.com

BUG=
LOG=N

Review-Url: https://codereview.chromium.org/2111873002
Cr-Commit-Position: refs/heads/master@{#37442}