perf top tui: Don't recalc column widths considering just the first page

It makes sense for the stdio where we can't navigate to the other pages.

On the TUI it breaks as soon as we navigate to other pages that have,
DSOs with longer names than the ones on the first page.

Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Mike Galbraith <efault@gmx.de>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Stephane Eranian <eranian@google.com>
Link: http://lkml.kernel.org/n/tip-zvqfp18mw229agb43cikgb0k@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>