powerpc/85xx: Remove stale BUG_ON in mpc85xx_smp_init

Under the FSL Hypervisor we triggered a BUG_ON in mpc85xx_smp_init that
expected smp_ops.message_pass to be explicity set.  However recent
changes allows smp_ops.message_pass to be NULL and handled by default
code.  Thus the BUG_ON isn't relevant anymore.

Signed-off-by: Laurentiu TUDOR <Laurentiu.Tudor@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>