HID: picoLCD: optimize for inactive debugfs

Matthieu CASTET adjusted picolcd_debug_out_report() to only operate when
there is an active listener on debugfs for events.

His change got lost while splitting hid_picolcd.c, restore it.

Signed-off-by: Bruno Prémont <bonbons@linux-vserver.org>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>