perf top: Fix uninitialized 'counter' variable

perf top: Fix uninitialized 'counter' variable

builtin-top.c has an uninitialized variable.
gcc(version 4.5.1) warns about it and it results in build failure:

 builtin-top.c: In function 'display_thread':
 builtin-top.c:518:9: error: 'counter' may be used uninitialized

This situation can indeed trigger, if the getline() call in
prompt_integer() fails.

Signed-off-by: Akihiro Nagai <[email protected]>
Cc: Arnaldo Carvalho de Melo <[email protected]>
Cc: Masami Hiramatsu <[email protected]>
Cc: Paul Mackerras <[email protected]>
Cc: Peter Zijlstra <[email protected]>
LKML-Reference: <20110323072939[email protected]>
Signed-off-by: Ingo Molnar <[email protected]>