smsc911x: Add check for ioremap_nocache() return code

There is no check for return code of smsc911x_drv_probe()
in smsc911x_drv_probe(). The patch adds one.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: David S. Miller <davem@davemloft.net>