perf machine: Propagate machine__init() error to callers

perf machine: Propagate machine__init() error to callers

machine__init() always returns 0 even when memory allocation fails,
because commit 81f981d7ec43ed93 ("perf machine: Free root_dir in
machine__init() error path") introduced 'int err = -ENOMEM' and an
error cleanup path but left the final 'return 0' instead of
'return err'.

Fix by returning err, check the return value in __machine__new_host()
which was ignoring it, and change machines__init() from void to int so
it too can propagate the error to perf_session__new(), aslr_tool__init()
and test callers.

The error cleanup also used zfree(&machine->kmaps), but kmaps is a
refcounted maps structure — use maps__zput() to properly drop the
reference, matching machine__exit().

Move dsos__init() and threads__init() before the first fallible
allocation (maps__new) so that machine__exit() is safe to call on
any machine struct that machine__init() touched, even on early failure.

Fixes: 81f981d7ec43ed93 ("perf machine: Free root_dir in machine__init() error path")
Reported-by: sashiko-bot <sashiko-bot@kernel.org>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Assisted-by: Claude:claude-opus-4.6
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>