Documentation/sysctl/vm.txt: fix misleading code reference of overcommit_memory

The origin document references to cap_vm_enough_memory is because
cap_vm_enough_memory invoked __vm_enough_memory before and it no longer
does now.
Signed-off-by: NChun Chen <ramichen@tencent.com>
Acked-by: NMichal Hocko <mhocko@suse.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

Documentation/sysctl/vm.txt

@@ -639,7 +639,7 @@ and don't use much of it.
 The default value is 0.
 
 See Documentation/vm/overcommit-accounting and
-security/commoncap.c::cap_vm_enough_memory() for more information.
+mm/mmap.c::__vm_enough_memory() for more information.
 
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