Wrong results in FMA when multiplier_mode is on

[jingpu]

commit ee81703

To reproduce:

make -f $FPGEN/Makefile run RUN="+NumTrans=1000 +Wave" GENESIS_PARAMS="top_FPGen.FPGen.FMA.PipelineDepth=8 top_FPGen.FPGen.FMA.EnableMultiplePumping=YES top_FPGen.FPGen.FMA.MulpPipelineDepth=3 top_FPGen.FPGen.FMA.MulShift.MUL0.TreeType=ZM top_FPGen.FPGen.FMA.MulShift.MUL0.BoothType=3"

Log:

51500: Transaction #25: 
51500 opcode: 01
51500 C is forwarded from Transaction #18
51501: SENT:   TypeA=PointOneOneOne SignA=0 ExpA=0x3fe FracA=0xfffffffffffff
51501:         TypeB=PointOneOneOne SignB=0 ExpB=0x3fe FracB=0xfffffffffffff
51501:         TypeC=Random SignC=0 ExpC=0x705 FracC=0x7d313777436c1
51501: EXPECTED: Type=Random Sign=0 Exp=0x3fe Frac=0xffffffffffffe
51501: FOUND:   Type=Random Sign=0 Exp=0x3fe Frac=0x6ccf51b711424
51501: 3fefffffffffffffx3fefffffffffffff+7057d313777436c1 = 3fe6ccf51b711424 (3feffffffffffffe) WRONG
51501: ERROR Found