loop: Remove duplicate assignments

The assignment and operation there will be overwritten later, so
it should be deleted.

The clang_analyzer complains as follows:

drivers/block/loop.c:2330:2 warning:

Value stored to 'err' is never read

change in v2:

Repair the sending email box

Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: luo penghao <luo.penghao@zte.com.cn>
Link: https://lore.kernel.org/r/20211104064546.3074-1-luo.penghao@zte.com.cn


Signed-off-by: Jens Axboe <axboe@kernel.dk>