crypto: sha512_ssse3 - fix byte count to bit count conversion

Byte-to-bit-count computation is only partly converted to big-endian and is
mixing in CPU-endian values. Problem was noticed by sparce with warning:

  CHECK   arch/x86/crypto/sha512_ssse3_glue.c
arch/x86/crypto/sha512_ssse3_glue.c:144:19: warning: restricted __be64 degrades to integer
arch/x86/crypto/sha512_ssse3_glue.c:144:17: warning: incorrect type in assignment (different base types)
arch/x86/crypto/sha512_ssse3_glue.c:144:17:    expected restricted __be64 <noident>
arch/x86/crypto/sha512_ssse3_glue.c:144:17:    got unsigned long long

Cc: <stable@vger.kernel.org>
Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>
Acked-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>