mpeg2enc: Fix compiler warning with clang

gstmpeg2enc.cc:224:5: warning: variable 'n' is incremented both in the loop header and in the loop body [-Wfor-loop-analysis]
    n++;
    ^
gstmpeg2enc.cc:221:29: note: incremented here
  for (n = 0; fpss[n] != 0; n++) {
                            ^
1 file changed