HID: sony: Perform a boundry check on the sixaxis battery level index.

Make sure that an out-of-bounds read doesn't occur in the Sixaxis battery level
lookup table in the event that the controller sends an invalid battery status
value in the report.

Signed-off-by: Frank Praznik <frank.praznik@oh.rr.com>
Reviewed-by: David Herrmann <dh.herrmann@gmail.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>