block: drop needless assignment in set_task_ioprio()

Commit 5fc11eeb ("block: open code create_task_io_context in
set_task_ioprio") introduces a needless assignment
'ioc = task->io_context', as the local variable ioc is not further
used before returning.

Even after the further fix, commit a957b612 ("block: fix error in
handling dead task for ioprio setting"), the assignment still remains
needless.

Drop this needless assignment in set_task_ioprio().

This code smell was identified with 'make clang-analyzer'.

Fixes: 5fc11eeb

 ("block: open code create_task_io_context in set_task_ioprio")
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Link: https://lore.kernel.org/r/20211223125300.20691-1-lukas.bulwahn@gmail.com


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