crypto: powerpc/sha - remove duplicate hash init function

sha*_base_init() series functions has implemented the initialization
of the hash context, this commit use sha*_base_init() function to
replace repeated implementations.

Signed-off-by: Tianjia Zhang <tianjia.zhang@linux.alibaba.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>