printf: implicate test line in failure messages

printf: implicate test line in failure messages

This improves the failure output by pointing to the failing line at the
top level of the test, e.g.:
      # test_number: EXPECTATION FAILED at lib/printf_kunit.c:103
  lib/printf_kunit.c:167: vsnprintf(buf, 256, "%#-12x", ...) wrote '0x1234abcd  ', expected '0x1234abce  '
      # test_number: EXPECTATION FAILED at lib/printf_kunit.c:142
  lib/printf_kunit.c:167: kvasprintf(..., "%#-12x", ...) returned '0x1234abcd  ', expected '0x1234abce  '

Signed-off-by: Tamir Duberstein <tamird@gmail.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Tested-by: Petr Mladek <pmladek@suse.com>
Link: https://lore.kernel.org/r/20250307-printf-kunit-convert-v6-3-4d85c361c241@gmail.com
Signed-off-by: Kees Cook <kees@kernel.org>