staging/rts_pstor: fix Polling thread wakeups CPU

RealTek PCI-E Card Reader rts_pstor driver causes CPU wakeup very
frequently, thatt's bad for power consumption.

Signed-off-by: Cho, Yu-Chen <acho@novell.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>