HID: sony: Fix Sixaxis cable state detection

Byte 31 of the Sixaxis report can change depending on whether or not the
controller is rumbling.  Using bit 3 is the only reliable way to detect the
state of the cable regardless of rumble activity.

Signed-off-by: Frank Praznik <frank.praznik@oh.rr.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>