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

drivers/crypto/bcm/cipher.c: In function 'handle_ahash_req':
drivers/crypto/bcm/cipher.c:720:15: warning:
 variable 'chunk_start' set but not used [-Wunused-but-set-variable]

drivers/crypto/bcm/cipher.c: In function 'spu_rx_callback':
drivers/crypto/bcm/cipher.c:1679:31: warning:
 variable 'areq' set but not used [-Wunused-but-set-variable]

drivers/crypto/bcm/cipher.c:1678:22: warning:
 variable 'ctx' set but not used [-Wunused-but-set-variable]

Fixes: 9d12ba86 ("crypto: brcm - Add Broadcom SPU driver")
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Reviewed-by: Raveendra Padasalagi <raveendra.padasalagi@broadcom.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>