perf ui browser: Fix scrollbar refresh row index

perf ui browser: Fix scrollbar refresh row index

The ui_browser__gotorc function needs offset from 'y' member, so the row
index has to begin with 0, which happens by accident in current code,
because we display only one header line.

The bug shows when we want to display more than 1 header lines like
columns headers in following patches.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Cc: Corey Ashford <cjashfor@linux.vnet.ibm.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1403178076-14072-4-git-send-email-jolsa@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>