mmap: fix error paths with dup_anon_vma()

When the calling function fails after the dup_anon_vma(), the
duplication of the anon_vma is not being undone.  Add the necessary
unlink_anon_vma() call to the error paths that are missing them.

This issue showed up during inspection of the error path in vma_merge()
for an unrelated vma iterator issue.

Users may experience increased memory usage, which may be problematic as
the failure would likely be caused by a low memory situation.

Link: https://lkml.kernel.org/r/20230929183041.2835469-3-Liam.Howlett@oracle.com
Fixes: d4af56c5

 ("mm: start tracking VMAs with maple tree")
Signed-off-by: Liam R. Howlett <Liam.Howlett@oracle.com>
Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Jann Horn <jannh@google.com>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>