bsg: remove unnecessary conditional expressions

Second condition in OR always implies first condition is false
thus bytes_read in the second is not needed. The same goes to
bytes_written.

Signed-off-by: Namhyung Kim <namhyung@gmail.com>
Acked-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>