replace reduce of syndrome_check by atomicAdd,
total time drop from 10.7 ms to 8.2 ms (save 23%)
8.2 ms for 36 iteration
nvprof
==9932== Profiling application: ldpc_bch_dvb-s2
==9932== Profiling result:
Time(%)      Time  Calls   Avg       Min       Max     Name
 49.15%  35.304ms  358  98.614us  71.424us  108.70us  updateCheckNode
 33.00%  23.700ms  358  66.199us  63.744us  68.992us  updateVariableNode
 15.39%  11.057ms  358  30.886us  29.120us  32.352us  syndrome_check
  1.09%  784.16us  368  2.1300us  1.8240us  11.392us  [CUDA memcpy DtoH]
  0.94%  677.09us   18  37.616us  1.3440us  191.68us  [CUDA memcpy HtoD]
  0.23%  167.17us   10  16.716us  16.448us  17.696us  initializeMVC_kernel
  0.19%  135.78us    5  27.155us  3.9680us  44.384us  [CUDA memset]