EFAULT seems to be much more appropriate error code for DMA mapping
failure, it also produces more informative message, compare:

ping 192.168.53.7
WARNING: eth0: No MAC address set. Using random address 92:4e:f1:18:96:67
eth0: 100Mbps full duplex link detected
ping failed: Bad address

versus old message:

ping 192.168.53.7
WARNING: eth0: No MAC address set. Using random address c6:b7:67:bb:4a:c3
eth0: 100Mbps full duplex link detected
ping failed: I/O error

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>