s390/qeth: handle error when backing RX buffer

qeth_init_qdio_queues() fills the RX ring with an initial set of
RX buffers. If qeth_init_input_buffer() fails to back one of the RX
buffers with memory, we need to bail out and report the error.

Fixes: 4a71df50 ("qeth: new qeth device driver")
Signed-off-by: Julian Wiedmann <jwi@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>