perf trace: Beautify new write hint fcntl commands

Those introduced by the commit c75b1d94 ("fs: add fcntl() interface for
setting/getting write life time hints"), tested using the proggie in that
commit comment:

  # perf trace -e fcntl ./write_hint write_hint.c
  fcntl: F_GET_RW_HINT: Invalid argument
     0.000 ( 0.006 ms): write_hint/7576 fcntl(fd: 3, cmd: GET_RW_HINT, arg: 0x7ffc6c918da0) = -1 EINVAL Invalid argument
     0.014 ( 0.004 ms): write_hint/7576 fcntl(fd: 4, cmd: GETFL) = 33794
  # perf trace -e fcntl ./write_hint write_hint.c 1
  fcntl: F_SET_RW_HINT: Invalid argument
     0.000 ( 0.007 ms): write_hint/7578 fcntl(fd: 3, cmd: SET_RW_HINT, arg: 0x7fff03866d70) = -1 EINVAL Invalid argument
     0.019 ( 0.002 ms): write_hint/7578 fcntl(fd: 4, cmd: GETFL) = 33794
  #

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Martin K. Petersen <martin.petersen@oracle.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-iacglkc99cchou87k62736dn@git.kernel.org


Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>