clang: suppress warnings

Initialize variables explicitly.

    ii.c:3249:21: warning: variable 'dcn0' is used uninitialized whenever '||'
          condition is true [-Wsometimes-uninitialized]
                    if (!actual_db0_chunk_size ||
                        ^~~~~~~~~~~~~~~~~~~~~~
    ii.c:3252:56: note: uninitialized use occurs here
      ...fake_map2(ctx, ii->chunk, &dw0, dc0, dcn0, actual_db0_chunk_size);
                                              ^~~~
    ii.c:3249:21: note: remove the '||' if its condition is always false
                    if (!actual_db0_chunk_size ||
                        ^~~~~~~~~~~~~~~~~~~~~~~~~
    ii.c:3222:50: note: initialize the variable 'dcn0' to silence this warning
      uint32_t dps0, dps1, dls0, dls1, sps, scn, dcn0, dcn1;
                                                     ^
                                                      = 0
    ii.c:3261:27: warning: variable 'dcn1' is used uninitialized whenever '||'
          condition is true [-Wsometimes-uninitialized]
                          if (!actual_db1_chunk_size ||
                              ^~~~~~~~~~~~~~~~~~~~~~
    ii.c:3263:62: note: uninitialized use occurs here
      ...fake_map2(ctx, ii->chunk, &dw1, dc1, dcn1, actual_db1_chunk_size);
                                              ^~~~
    ii.c:3261:27: note: remove the '||' if its condition is always false
                          if (!actual_db1_chunk_size ||
                              ^~~~~~~~~~~~~~~~~~~~~~~~~
    ii.c:3222:56: note: initialize the variable 'dcn1' to silence this warning
      uint32_t dps0, dps1, dls0, dls1, sps, scn, dcn0, dcn1;
                                                           ^
                                                            = 0