staging: rtl8192e: Modify time handling

In several places, the driver keeps times (in jiffies) in two 32-bit
quantities. In the rtl8192_hw_to_sleep(), there is an error in the
calculation of the difference between two 64-bit quantities. Rather
than fix that error, I have converted to a single 64-bit number. That
makes the code be much cleaner and clearer.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>