tg3: Dont dump DMA error when interface not ready.

tg3: Dont dump DMA error when interface not ready.

This fixes orabug 12981473.

When do testing with BCM5704 Gigabit Ethernet, bootup get below warning:

tg3 0000:03:01.0: eth0: DMA Status error.  Resetting chip.
<Registers state of device>
tg3 0000:03:01.0: eth0: 0: Host status block [00000007:00000002:(0000:0000:0000):(0000:0000)]
tg3 0000:03:01.0: eth0: 0: NAPI info [00000001:00000002:(0000:0000:01ff):0000:(00c8:0000:0000:0000)]
tg3 0000:03:01.0: eth0: Link is up at 1000 Mbps, full duplex
tg3 0000:03:01.0: eth0: Flow control is on for TX and on for RX
tg3 0000:03:01.0: tg3_stop_block timed out, ofs=4800 enable_bit=2
tg3 0000:03:01.0: eth0: Link is down
tg3 0000:03:01.0: eth0: Link is up at 1000 Mbps, full duplex
tg3 0000:03:01.0: eth0: Flow control is on for TX and on for RX

We need not to check the status and dump registers status if the device
not ready,

Signed-off-by: Joe Jin <joe.jin@oracle.com>
Reported-by: Gurudas Pai <gurudas.pai@oracle.com>