[PATCH] spufs: fix context-switch decrementer code

We found that when the 'decrementer' is saved, the PPE saves the current
time 'csa->suspend_time'. When restoring the 'decrementer', (Step 34)
decrementer seems to be adjusted with the number of cycles th= at a spu
thread has not been running.

In that code it is missing a substract ('-') because 'delta_time' is
assigned a not substracted(see bellow).

Acked-by: Mark Nutter <mnutter@us.ibm.com>
Signed-off-by: Arnd Bergmann <arnd.bergmann@de.ibm.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>