Fix declaration of cgroup_mm_owner_callbacks()
The choice of real/dummy declaration for cgroup_mm_owner_callbacks()
shouldn't be based on CONFIG_MM_OWNER, but on
CONFIG_CGROUPS. Otherwise kernel/exit.c fails to compile when
something other than a cgroups controller selects CONFIG_MM_OWNER
Signed-off-by: Paul Menage <menage@xxxxxxxxxx>
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This is a retry with a mailer that hopefully didn't break the
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