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: Chun Chen <[e-mail]>
Acked-by: Michal Hocko <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

Documentation/sysctl/vm.txt

···
 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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