perf annotate browser: Use struct annotation_line in find functions

perf annotate browser: Use struct annotation_line in find functions

Use struct annotation_line in find functions:

  annotate_browser__find_string
  annotate_browser__find_string_reverse

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Andi Kleen <andi@firstfloor.org>
Cc: David Ahern <dsahern@gmail.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/20171011150158.11895-33-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>