selftests: ipc: Replace fail print statements with ksft_test_result_fail

Use the standard kselftest failure report function to ensure consistent
test output formatting. This improves readability and integration with
automated test frameworks.

Link: https://lore.kernel.org/r/20250531070140.24287-1-sef1548@gmail.com


Signed-off-by: Nick Huang <sef1548@gmail.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>