erasure-code: var-sized array init is done separatly.

erasure-code: var-sized array init is done separatly.

```
/home/jenkins/workspace/ceph-master/src/erasure-code/clay/ErasureCodeClay.cc:391:21: error: variable-sized object may not be initialized
  int weight_vector[t] = {0};
                    ^
1 error generated.
```
And GCC doesn't like:
```
  weight_vector = {0};
```

So use std:fill()

Signed-off-by: Willem Jan Withagen <wjw@digiware.nl>