Eliminate sparse warning - bad constant expression

Eliminiate sparse warning during usage of crypto_shash_* APIs
       error: bad constant expression

Allocate memory for shash descriptors once, so that we do not kmalloc/kfree it
for every signature generation (shash descriptor for md5 hash).

From ed7538619817777decc44b5660b52268077b74f3 Mon Sep 17 00:00:00 2001
From: Shirish Pargaonkar <shirishpargaonkar@gmail.com>
Date: Tue, 24 Aug 2010 11:47:43 -0500
Subject: [PATCH] eliminate sparse warnings during crypto_shash_* APis usage

Signed-off-by: Shirish Pargaonkar <shirishpargaonkar@gmail.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>