perf hists browser: Do not exit when 'f' is pressed in 'report' mode

perf hists browser: Do not exit when 'f' is pressed in 'report' mode

The 'f' hotkey is only used when in 'top', dynamic mode, to
enable/disable events, currently not making sense in the 'report',
static mode, where we can't go from showing the histogram entries
created from a perf.data file to adding more events after recreating the
evlist created from the perf.data file, albeit possible, this is not
implemented right now.

Cc: Adrian Hunter <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: David Ahern <[email protected]>
Cc: Don Zickus <[email protected]>
Cc: Frederic Weisbecker <[email protected]>
Cc: Jiri Olsa <[email protected]>
Cc: Namhyung Kim <[email protected]>
Cc: Stephane Eranian <[email protected]>
Link: http://lkml.kernel.org/n/[email protected]
Signed-off-by: Arnaldo Carvalho de Melo <[email protected]>