powerpc/85xx: Fix support for enabling doorbells for IPIs

Commit 765342526246c97600e5344c0949824d94bb51c3 made some small changes to
IPI, message_pass in smp_ops was initialized to NULL for other platforms
but not for 85xx which causes us to always use the mpic for IPI's even
if we support doorbells in HW.

Signed-off-by: Matthew McClintock <msm@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>

arch/powerpc/platforms/85xx/smp.c

@@ -243,6 +243,7 @@ void __init mpc85xx_smp_init(void)
 		 * If left NULL, .message_pass defaults to
 		 * smp_muxed_ipi_message_pass
 		 */
+		smp_85xx_ops.message_pass = NULL;
 		smp_85xx_ops.cause_ipi = doorbell_cause_ipi;
 	}