tools: fix atomic_set() definition to set the value correctly

Currently vma test is failing because of the new vma_assert_attached()
assertion.  The check is failing because previous refcount_set() inside
vma_mark_attached() is a NoOp.  Fix the definition of atomic_set() to
correctly set the value of the atomic.

Link: https://lkml.kernel.org/r/20241227222220.1726384-1-surenb@google.com


Fixes: 9325b8b5 ("tools: add skeleton code for userland testing of VMA logic")
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Reviewed-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
Cc: Jann Horn <jannh@google.com>
Cc: Liam R. Howlett <Liam.Howlett@Oracle.com>
Cc: Vlastimil Babka <vbabka@suse.cz>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>