net: axienet: Propagate failure of DMA descriptor setup

When we fail allocating the DMA buffers in axienet_dma_bd_init(), we
report this error, but carry on with initialisation nevertheless.

This leads to a kernel panic when the driver later wants to send a
packet, as it uses uninitialised data structures.

Make the axienet_device_reset() routine return an error value, as it
contains the DMA buffer initialisation. Make sure we propagate the error
up the chain and eventually fail the driver initialisation, to avoid
relying on non-initialised buffers.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Radhey Shyam Pandey <radhey.shyam.pandey@xilinx.com>
Signed-off-by: David S. Miller <davem@davemloft.net>