mbsys_simrad3_zero_ss had for i inside of for i

[schwehr]

Definitely not going to zero all the things

for (int i = 0; i < MBSYS_SIMRAD3_NUM_PING_STRUCTURES; i++) {
  // ...
  for (int i = 0; i < MBSYS_SIMRAD3_MAXBEAMS; i++) {
    //
  }
  for (int i = 0; i < MBSYS_SIMRAD3_MAXRAWPIXELS; i++) {
    //
  }
  for (int i = 0; i < MBSYS_SIMRAD3_MAXPIXELS; i++) {
     //
  }
}