selftests: ublk: kublk: fix an error log line

When doing io_uring operations using liburing, errno is not used to
indicate errors, so the %m format specifier does not provide any
relevant information for failed io_uring commands. Fix a log line
emitted on get_params failure to translate the error code returned in
the cqe->res field instead.

Signed-off-by: Uday Shankar <ushankar@purestorage.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/20250401-ublk_selftests-v1-2-98129c9bc8bb@purestorage.com


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