Fix block_suspend denial for slideshow

Add wakelock_use to slideshow.te to fix the following denial:

avc:  denied  { block_suspend } for  pid=137 comm="slideshow" capability=36  scontext=u:r:slideshow:s0 tcontext=u:r:slideshow:s0 tclass=capability2 permissive=0

Change-Id: If84f167cd235e8196eadf3fb85cc725a5ea464e6