mm: kmsan: apply __must_check to non-void functions

Non-void KMSAN hooks may return error codes that indicate that KMSAN
failed to reflect the changed memory state in the metadata (e.g.  it could
not create the necessary memory mappings).  In such cases the callers
should handle the errors to prevent the tool from using the inconsistent
metadata in the future.

We mark non-void hooks with __must_check so that error handling is not
skipped.

Link: https://lkml.kernel.org/r/20230413131223.4135168-3-glider@google.com


Signed-off-by: Alexander Potapenko <glider@google.com>
Reviewed-by: Marco Elver <elver@google.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Dipanjan Das <mail.dipanjan.das@gmail.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: Uladzislau Rezki (Sony) <urezki@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>