docs: update link to powerpc/vmemmap_dedup.rst

after move of powerpc/ to arch/
Signed-off-by: Costa Shulyupin <costa.shul@redhat.com>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20230927164319.2686237-1-costa.shul@redhat.com

Documentation/mm/vmemmap_dedup.rst

@@ -211,7 +211,7 @@ the device (altmap).
 
 The following page sizes are supported in DAX: PAGE_SIZE (4K on x86_64),
 PMD_SIZE (2M on x86_64) and PUD_SIZE (1G on x86_64).
-For powerpc equivalent details see Documentation/powerpc/vmemmap_dedup.rst
+For powerpc equivalent details see Documentation/arch/powerpc/vmemmap_dedup.rst
 
 The differences with HugeTLB are relatively minor.