fs, proc: remove priv argument from is_stack

fs, proc: remove priv argument from is_stack

Commit b18cb64ead40 ("fs/proc: Stop trying to report thread stacks")
removed the priv parameter user in is_stack so the argument is
redundant.  Drop it.

[[email protected]: remove unused variable]
Link: http://lkml.kernel.org/r/[email protected]
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Michal Hocko <[email protected]>
Signed-off-by: Arnd Bergmann <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>