engines/io_uring: Fix negative errno in io_u->error

engines/io_uring: Fix negative errno in io_u->error

io_u->error can have either negative errno value or device-specific
error status as a positive value.  fio always tries to parse the errno
with strerrno() and it expects the value to be a positive one.

Commit ebe67b667f25 ("io_uring: Add IO_U_F_DEVICE_ERRROR to identify
error types") tried to abs(io_u->error) to convert it first.  And it
caused the following build warning:

  engines/io_uring.c:553:16: error: taking the absolute value of unsigned type 'unsigned int' has no effect [-Werror,-Wabsolute-value]
          io_u->error = abs(io_u->error);
                        ^
  engines/io_uring.c:553:16: note: remove the call to 'abs' since unsigned values cannot be negative
          io_u->error = abs(io_u->error);
                        ^~~

Commit 9eaa8e7c8e0b ("engines/io_uring: don't use abs() on an unsigned
value") tried to remove the warning by removing abs() on io_u->error,
but if so, negative errno (e.g., -EINVAL) can't be parsed properly like:

  fio: io_u error on file /dev/ng0n1: Unknown error -22: write offset=429916160, buflen=1048576

This patch fixed this fixed to convert to positive value properly by
casting it first to int and then do abs() on it.

Fixes: 9eaa8e7c8e0b ("engines/io_uring: don't use abs() on an unsigned value")

Signed-off-by: Minwoo Im <minwoo.im.dev@gmail.com>
Link: https://lore.kernel.org/r/20240927030857.17001-1-minwoo.im.dev@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>