crypto: marvell - remove set but not used variable 'index'

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

drivers/crypto/marvell/hash.c: In function 'mv_cesa_ahash_pad_req':
drivers/crypto/marvell/hash.c:138:15: warning: variable 'index' set but not used [-Wunused-but-set-variable]

It's never used and can be removed.

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Mukesh Ojha <mojha@codeaurora.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>