kselftest/mm: clarify errors for pipe()

kselftest/mm: clarify errors for pipe()

Patch series "selftests/mm: Tweaks to the cow test".

A collection of non-functional updates from David Hildenbrand's review.

This patch (of 4):

Specify that errors reported from pipe() failures are the result of
failures.

Link: https://lkml.kernel.org/r/20250610-selftest-mm-cow-tweaks-v1-0-43cd7457500f@kernel.org
Link: https://lkml.kernel.org/r/20250610-selftest-mm-cow-tweaks-v1-1-43cd7457500f@kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>
Suggested-by: David Hildenbrand <david@redhat.com>
Acked-by: David Hildenbrand <david@redhat.com>
Cc: Mark Brown <broonie@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>