erasure-code: No need to zero padding data.

This only happen when last encode. The size of padding data don't
include the size of object. When read, we can't read this padding data.
So don't care the content of this padding data.
Signed-off-by: Ma Jianpeng <jianpeng.ma@intel.com>
erasure-code: No need do rebuild_page_aligned.

Although do erasure-encode need align memory, the rebuild_page_aligned
don't this. In encode_chunks, it make the encode data memory address
aligned.

Signed-off-by: Ma Jianpeng <jianpeng.ma@intel.com>