[POWERPC] spufs: fix initial state of wbox file

The wbox channel count of an spu is now initialized
to four for the saved context. This makes it possible
to write to the mailbox right away without waiting
for the SPE to become scheduled first.
Signed-off-by: NArnd Bergmann <arnd.bergmann@de.ibm.com>
Signed-off-by: NPaul Mackerras <paulus@samba.org>

arch/powerpc/platforms/cell/spufs/switch.c

@@ -2129,6 +2129,7 @@ static void init_prob(struct spu_state *csa)
 	csa->spu_chnlcnt_RW[28] = 1;
 	csa->spu_chnlcnt_RW[30] = 1;
 	csa->prob.spu_runcntl_RW = SPU_RUNCNTL_STOP;
+	csa->prob.mb_stat_R = 0x000400;
 }
 
 static void init_priv1(struct spu_state *csa)