perf lock: Fix option value type in parse_max_stack

perf lock: Fix option value type in parse_max_stack

The value is a void* and the address of an int, max_stack_depth, is
set up in the perf lock options. The parse_max_stack function treats
the int* as a long*, make this more correct by declaring the value to
be an int*.

Fixes: 0a277b622670 ("perf lock contention: Check --max-stack option")
Signed-off-by: Ian Rogers <irogers@google.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>