perf top: Display slow reader warning when droping samples

Currently we display the "Too slow to read ring buffer.." helpline only
in the slow reader thread. This patch triggers it also when the
processing thread drops samples, because it has the same reason, which
is too many data on input.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Acked-by: David S. Miller <davem@davemloft.net>
Acked-by: Namhyung Kim <namhyung@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lkml.kernel.org/n/tip-bnev2mloavyurmgchcr3o24o@git.kernel.org


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