crypto: scatterwalk - remove duplicate function declarations

scatterwalk_map() is an inline function already defined in the
header file, it is necessary to delete the re-declaration at the
same location, which was left out in the header file by an
earlier modification.

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