selftests: mm: check return values

Check return value and return error/skip the tests.

Link: https://lkml.kernel.org/r/20240520185248.1801945-1-usama.anjum@collabora.com


Fixes: 46fd75d4 ("selftests: mm: add pagemap ioctl tests")
Signed-off-by: Muhammad Usama Anjum <usama.anjum@collabora.com>
Cc: Shuah Khan <shuah@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>