ethernet: atl1: Add missing DMA mapping error checks and count errors

ethernet: atl1: Add missing DMA mapping error checks and count errors

The `dma_map_XXX()` functions can fail and must be checked using
`dma_mapping_error()`.  This patch adds proper error handling for all
DMA mapping calls.

In `atl1_alloc_rx_buffers()`, if DMA mapping fails, the buffer is
deallocated and marked accordingly.

In `atl1_tx_map()`, previously mapped buffers are unmapped and the
packet is dropped on failure.

If `atl1_xmit_frame()` drops the packet, increment the tx_error counter.

Fixes: f3cc28c79760 ("Add Attansic L1 ethernet driver.")
Signed-off-by: Thomas Fourier <fourier.thomas@gmail.com>
Link: https://patch.msgid.link/20250625141629.114984-2-fourier.thomas@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>