perf trace: Beautify fifth argument of mmap() as fd

perf trace: Beautify fifth argument of mmap() as fd

The fifth argument of mmap syscall is fd and it often contains -1 as a
value for anon mappings.  Without this patch it doesn't show the file
name as well as it shows -1 as 4294967295.

Signed-off-by: Namhyung Kim <[email protected]>
Acked-by: David Ahern <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>