selftests/mm: guard-regions: Use SKIP() instead of ksft_exit_skip()

selftests/mm: guard-regions: Use SKIP() instead of ksft_exit_skip()

To ensure only the current test is skipped on permission failure, instead
of terminating the entire test binary.

Link: https://lkml.kernel.org/r/20250717131857.59909-3-lianux.mm@gmail.com
Signed-off-by: wang lian <lianux.mm@gmail.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Acked-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Reviewed-by: Wei Yang <richard.weiyang@gmail.com>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Jann Horn <jannh@google.com>
Cc: Kairui Song <ryncsn@gmail.com>
Cc: Liam Howlett <liam.howlett@oracle.com>
Cc: SeongJae Park <sj@kernel.org>
Cc: Shuah Khan <shuah@kernel.org>
Cc: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>