Correct the wrong SNR calculation for DVB-S2.

Test:

SPACECAST2# dvbsnoop -s signal
dvbsnoop V1.4.50 -- http://dvbsnoop.sourceforge.net/

---------------------------------------------------------
Transponder/Frequency signal strength statistics...
---------------------------------------------------------
cycle: 1  d_time: 0.001 s  Sig: 31  SNR: 19  BER: 4009  UBLK: 0  Stat:
0x1f [SIG CARR VIT SYNC LOCK ]

Google-Bug-Id: 19432272
Change-Id: I38b0d0b065a2f1a48fdd59a7c00fc13e71e88012
1 file changed