powerpc/powernv: Fix return value from power7_nap() et al.

The power7_nap(), power7_sleep() and power7_winkle() functions are
called from pnv_smp_cpu_kill_self(), which expects them to return the
SRR1 value set by the hardware on wakeup, or 0 if no nap/sleep/winkle
occurred.  However, in the case where an interrupt needs to be
replayed, the logic in power7_powersave_common (the common code for
power7_nap et al.) doesn't set r3 to 0 in this case.  Instead what we
get as the return value is the selector for the type of power-saving
mode requested (1, 2 or 3).  In fact this should not affect the
operation of pnv_smp_cpu_kill_self(), but it is better to get this
correct, so this adds an instruction to set r3 to 0 in this case.
Signed-off-by: NPaul Mackerras <paulus@samba.org>
Signed-off-by: NMichael Ellerman <mpe@ellerman.id.au>

arch/powerpc/kernel/idle_power7.S

@@ -94,6 +94,7 @@ _GLOBAL(power7_powersave_common)
 	beq	1f
 	addi	r1,r1,INT_FRAME_SIZE
 	ld	r0,16(r1)
+	li	r3,0			/* Return 0 (no nap) */
 	mtlr	r0
 	blr