ocelot: Don't sleep in atomic context (irqs_disabled())

Preemption disabled at:
 [<ffff000008cabd54>] dev_set_rx_mode+0x1c/0x38
 Call trace:
 [<ffff00000808a5c0>] dump_backtrace+0x0/0x3d0
 [<ffff00000808a9a4>] show_stack+0x14/0x20
 [<ffff000008e6c0c0>] dump_stack+0xac/0xe4
 [<ffff0000080fe76c>] ___might_sleep+0x164/0x238
 [<ffff0000080fe890>] __might_sleep+0x50/0x88
 [<ffff0000082261e4>] kmem_cache_alloc+0x17c/0x1d0
 [<ffff000000ea0ae8>] ocelot_set_rx_mode+0x108/0x188 [mscc_ocelot_common]
 [<ffff000008cabcf0>] __dev_set_rx_mode+0x58/0xa0
 [<ffff000008cabd5c>] dev_set_rx_mode+0x24/0x38

Fixes: a556c76a ("net: mscc: Add initial Ocelot switch support")

Signed-off-by: Claudiu Manoil <claudiu.manoil@nxp.com>
Signed-off-by: David S. Miller <davem@davemloft.net>