perf report/top TUI: Fix title line formatting

perf report/top TUI: Fix title line formatting

In d10ec006dcd7 ("perf hists browser: Allow passing an initial hotkey")
the hist_entry__title() call was cut'n'pasted to a function where the
'title' variable is a pointer, not an array, so the sizeof(title)
continues syntactically valid but ends up reducing the real size of the
buffer where to format the first line in the screen to 8 bytes, which
makes the formatting at the title at each refresh to produce just the
string "Samples ", duh, fix it by passing the size of the buffer.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Jin Yao <yao.jin@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Fixes: d10ec006dcd7 ("perf hists browser: Allow passing an initial hotkey")
Link: http://lore.kernel.org/lkml/20200330154314.GB4576@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>