HID: picoLCD: Deletion of unnecessary checks before three function calls

The functions backlight_device_unregister(), lcd_device_unregister() and
rc_unregister_device() test whether their argument is NULL and then
return immediately. Thus the test around the call is not needed.

This issue was detected by using the Coccinelle software.

Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Reviewed-by: Bruno Prémont <bonbons@linux-vserver.org>
Signed-off-by: Jiri Kosina <jkosina@suse.com>