crypto: x86/des3 - remove redundant assignment of variable nbytes

The variable nbytes is being assigned a value that is never read, it is
being re-assigned in the following statement. The assignment is redundant
and can be removed.

Signed-off-by: Colin Ian King <colin.i.king@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>