net: ethernet: ec_bhf: Fix dma_free_coherent() dma handle

In the Linux kernel, the following vulnerability has been resolved: net: ethernet: ec_bhf: Fix dma_free_coherent() dma handle dma_free_coherent() in error path takes priv->rx_buf.alloc_len as the dma handle. This would lead to improper unmapping of the buffer. Change the dma handle to priv->rx_buf.alloc_phys.