list: test: Add test for list_del_init_careful()

The list_del_init_careful() function was added[1] after the list KUnit
test. Add a very basic test to cover it.

Note that this test only covers the single-threaded behaviour (which
matches list_del_init()), as is already the case with the test for
list_empty_careful().

[1]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=c6fe44d96fc1536af5b11cd859686453d1b7bfd1



Signed-off-by: David Gow <davidgow@google.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>