restore the vgpr pool, modified in openSumAtLeastUnroll(), in closeSumAtLeastUnroll() instead of in endSummation()
restore the vgpr pool, modified in openSumAtLeastUnroll(), in closeSumAtLeastUnroll() instead of in endSummation()

or it would cause vgpr aliasing when one obtains temporary vgprs in the tail loop

ROCmSoftwarePlatform/Tensile,ROCmSoftwarePlatform/Tensile,ROCmSoftwarePlatform/Tensile