perf tools: Fix dwarf unwind max_stack processing

perf tools: Fix dwarf unwind max_stack processing

The 'unwind__get_entries' function currently returns 'max_stack + 1'
entries (instead of exact max_stack entries), because max_stack value
does not get decremented for the first entry.

This fix makes dwarf-unwind test pass.

Signed-off-by: Jiri Olsa <jolsa@redhat.com>
Acked-by: Jean Pihet <jean.pihet@linaro.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jean Pihet <jean.pihet@linaro.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1389098853-14466-7-git-send-email-jolsa@redhat.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>