perf top: Add missing newline on pr_err call

perf top: Add missing newline on pr_err call

The perf_event__process_sample function, when not finding a machine
associated with a sample, was calling pr_err without a newline,
garbling the screen on TUI mode due to a problem introduced by a
recent ui_helpline patch.

On --stdio it would just concatenate the messages for each sample with
no machine associated, fix it by adding the newline.

Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Namhyung Kim <namhyung@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-vuz88welqvp15c2uybd9osnz@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>