perf tools: Ensure return negative value when write header error

When 'perf record' write headers, it calls write_xxx in
tools/perf/util/header.c, and check return value. It rolls back all
working only when return value is negative.

This patch ensures write_cpudesc() and write_total_mem() return negative number
when error. Without this patch, headers reported by 'perf report' header is
error in some platform. Following output is caputured on ARM, which doesn't
contain "Processor" field in /proc/cpuinfo. See "cpudesc", "total memory" and
"cmdline" field.

   bash-4.2# perf record ls
   ...
   [ perf record: Woken up 1 times to write data ]
   [ perf record: Captured and wrote 0.001 MB perf.data (~36 samples) ]
   bash-4.2# perf report --stdio --header
   Error:
   The perf.data file has no samples!
   # ========
   # captured on: Fri Sep 12 10:09:10 2014
   # hostname : arma15el
   # os release : 3.17.0+
   # perf version : 3.10.53
   # arch : armv7l
   # nrcpus online : 4
   # nrcpus avail : 1
   # cpudesc : (null)
   # total memory : 0 kB
   # cmdline :
   # event : name = cycles, type = 0, config = 0x0, config1 = 0x0, config2 = 0x0, excl_usr = 0, excl_kern = 0, excl_host = 0, excl_guest = 1, precise_ip = 0
   # pmu mappings: not available
   # ========
   #

Cc: Adrian Hunter <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Li Zefan <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Waiman Long <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Wang Nan <[email protected]>
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>

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