perf top: Remove redundant 'err' variable

The variable 'err' in the perf_event__process_sample() is only used in
the only one judgment statement, it is not used in other places.

So, use the return value from hist_entry_iter__add() directly instead of
taking this in another redundant variable.

Signed-off-by: tangmeng <tangmeng@uniontech.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lore.kernel.org/lkml/20220216030425.27779-2-tangmeng@uniontech.com


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