net: axienet: Check for DMA mapping errors

[ Upstream commit 71791dc8bdea55eeb2a0caefe98a0b7450c6e0af ]

Especially with the default 32-bit DMA mask, DMA buffers are a limited
resource, so their allocation can fail.
So as the DMA API documentation requires, add error checking code after
dma_map_single() calls to catch the case where we run out of "low" memory.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Stable-dep-of: 9ff2f816e2aa ("net: axienet: Fix register defines comment description")
Signed-off-by: Sasha Levin <sashal@kernel.org>