Fix references to nommu-mmap.rst

nommu-mmap.rst was moved to Documentation/admin-guide/mm; this patch
updates the remaining stale references to Documentation/mm.

Fixes: 800c02f5d030 ("docs: move nommu-mmap.txt to admin-guide and rename to ReST")
Signed-off-by: Stephen Kitt <steve@sk2.org>
Link: https://lore.kernel.org/r/20200812092230.27541-1-steve@sk2.org
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
diff --git a/init/Kconfig b/init/Kconfig
index d6a0b31..c0f56e4 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1986,7 +1986,7 @@
 	  userspace.  Since that isn't generally a problem on no-MMU systems,
 	  it is normally safe to say Y here.
 
-	  See Documentation/mm/nommu-mmap.rst for more information.
+	  See Documentation/admin-guide/mm/nommu-mmap.rst for more information.
 
 config SYSTEM_DATA_VERIFICATION
 	def_bool n