x86_64: Fix comp-long
x86_64: Fix comp-long

If result and source are the same VR then implementation does
a wrong thing clearing dest in the beginning.

Change-Id: I66d97a828aa38121676561858119ccd44aaa4d50
Signed-off-by: Serguei Katkov <53c1eb3349c33a81de4c7fece05dd168a3eb410e@intel.com>

treadstoneproject/artinst,treadstoneproject/artinst,treadstoneproject/artinst,treadstoneproject/artinst,treadstoneproject/artinst