bs_ssc: remove unused variables

The variables, transfer_length and residue are never used in the
function tape_rdwr_request()

Signed-off-by: Ruoyu <liangry@ucweb.com>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
bs_rbd: fix error assignment in if condition

The statement

if ((x == f()) < 0) {}

is strange. I think it should be

if ((x = f()) < 0) {}

For the reasone of coding style, I modify it as

x = f();
if (x < 0) {}

Signed-off-by: Ruoyu <liangry@ucweb.com>
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>