selftests: android: ion: return Kselftest Skip code for skipped tests

selftests: android: ion: return Kselftest Skip code for skipped tests

When ion test is skipped because of unmet dependencies and/or unsupported
configuration, it returns 0 which is treated as a pass by the Kselftest
framework. This leads to false positive result even when the test could
not be run.

Change it to return kselftest skip code when a test gets skipped to
clearly report that the test could not be run.

Kselftest framework SKIP code is 4 and the framework prints appropriate
messages to indicate that the test is skipped.

Signed-off-by: Shuah Khan (Samsung OSG) <shuah@kernel.org>
Acked-by: Pintu Agarwal <pintu.ping@gmail.com>
Signed-off-by: Shuah Khan (Samsung OSG) <shuah@kernel.org>