bpf tools: Fix syscall argument

bpf tools: Fix syscall argument

Coverity flagged this under CID 1354884 as a sizeof mismatch, it turns
out that the argument "attr" passed to syscall should have been a
pointer to attr in the first place.

Reported-by: coverity (CID 1354884)
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Wang Nan <wangnan0@huawei.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Fixes: 8f9e05fb298f ("perf tools: Fix PowerPC native building")
Link: http://lkml.kernel.org/r/1461551694-5512-3-git-send-email-f.fainelli@gmail.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>