perf probe: Fix dwarf regs table for x86_64

In 293d5b43 ("perf probe: Support probing on offline cross-arch binary")
DWARF register tables were introduced for many architectures, with the one for
the "dx" register being broken for x86_64, which got noticed by the 'perf test
bpf' testcase, that has this difference from a successful run to one that
fails, with the aforementioned patch:

  -Writing event: p:perf_bpf_probe/func _text+5197232 f_mode=+68(%di):x32 offset=%si:s64 orig=dx:s32
  -Failed to write event: Invalid argument
  -bpf_probe: failed to apply perf probe eventsFailed to add events selected by BPF
  +Writing event: p:perf_bpf_probe/func _text+5197232 f_mode=+68(%di):x32 offset=%si:s64 orig=%dx:s32

Add the missing '%' to '%dx' to fix this.

Acked-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Wang Nan <wangnan0@huawei.com>
Fixes: 293d5b43 ("perf probe: Support probing on offline cross-arch binary")
Link: https://lkml.kernel.org/r/20160909145955.GC32585@kernel.org


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