crypto: ux500 - Remove set but not used variable 'cookie'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/crypto/ux500/hash/hash_core.c: In function hash_set_dma_transfer:
drivers/crypto/ux500/hash/hash_core.c:143:15: warning: variable cookie set but not used [-Wunused-but-set-variable]

It is not used since commit 8a63b199 ("crypto:
ux500 - Add driver for HASH hardware")

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: zhengbin <zhengbin13@huawei.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>