Remove the magic numbers used in sixaxis_set_operational_usb():
  - use the already defined SIXAXIS_REPORT_0xF2_SIZE;
  - define and use SIXAXIS_REPORT_0xF5_SIZE;
  - set the dummy buffer size to accommodate any report that is going to
    be requested.
Signed-off-by: NAntonio Ospite <ao2@ao2.it>
Acked-by: NFrank Praznik <frank.praznik@oh.rr.com>
Signed-off-by: NJiri Kosina <jkosina@suse.cz>