net: hip04: fix RX buffer leak on build_skb failure

net: hip04: fix RX buffer leak on build_skb failure

When build_skb() fails in hip04_rx_poll(), the driver jumps to the
refill path without releasing the current RX buffer and its DMA mapping.
Installing a replacement buffer then overwrites the slot references and
leaks both resources.

Keep the current slot intact and return budget so NAPI retries the same
buffer.  Also free a newly allocated RX fragment when dma_map_single()
fails.

This issue was found by an in-house static analysis tool.

Fixes: 701a0fd52318 ("hip04_eth: fix missing error handle for build_skb failed")
Cc: stable@vger.kernel.org
Signed-off-by: Fan Wu <fanwu01@zju.edu.cn>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Link: https://patch.msgid.link/20260712142729.2057636-1-fanwu01@zju.edu.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>