5255 uts shouldn't open-code ISP2

*** 3785,3795 ****
          }
  
          hdr = kobj_comphdr(file);
          if (hdr->ch_magic != CH_MAGIC_ZLIB || hdr->ch_version != CH_VERSION ||
              hdr->ch_algorithm != CH_ALG_ZLIB || hdr->ch_fsize == 0 ||
!             (hdr->ch_blksize & (hdr->ch_blksize - 1)) != 0) {
                  kobj_free(file->_dbuf, cip->fsize);
                  return (-1);
          }
          file->_base = kobj_alloc(hdr->ch_blksize, KM_WAIT|KM_TMP);
          file->_bsize = hdr->ch_blksize;
--- 3785,3795 ----
          }
  
          hdr = kobj_comphdr(file);
          if (hdr->ch_magic != CH_MAGIC_ZLIB || hdr->ch_version != CH_VERSION ||
              hdr->ch_algorithm != CH_ALG_ZLIB || hdr->ch_fsize == 0 ||
!             !ISP2(hdr->ch_blksize)) {
                  kobj_free(file->_dbuf, cip->fsize);
                  return (-1);
          }
          file->_base = kobj_alloc(hdr->ch_blksize, KM_WAIT|KM_TMP);
          file->_bsize = hdr->ch_blksize;