perf ui tui: Register the error callbacks before initializing the widgets

perf ui tui: Register the error callbacks before initializing the widgets

I.e. we want to tell the user about errors found during, for instance,
the ui_browser initialization, so that a call to ui__warning() appears
as a window waiting for a key to be pressed.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-ederrwizcl6mfz10vfobl5qq@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>