desc_81: Fix compilation with older compilers

The attached fixes the following error when compiling 'dvblastctl'

  /usr/local/include/bitstream/atsc/si/desc_81.h: In function ‘desc81_bit_rate_code_from_octetrate’:
  /usr/local/include/bitstream/atsc/si/desc_81.h:83:5: error: ‘for’ loop initial declarations are only allowed in C99 mode
  /usr/local/include/bitstream/atsc/si/desc_81.h:83:5: note: use option -std=c99 or -std=gnu99 to compile your code

Apply via 'git am 0001-desc_81-Fix-compilation-with-older-compilers.patch'
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