hw/net/xilinx_axienet: Remove unncessary cast

Remove unncessary cast, buf is already uint8_t *.
No functional change.

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Francisco Iglesias <frasse.iglesias@gmail.com>
Signed-off-by: Edgar E. Iglesias <edgar.iglesias@xilinx.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20200506082513.18751-4-edgar.iglesias@gmail.com>

hw/net/xilinx_axienet.c

@@ -918,7 +918,7 @@ xilinx_axienet_data_stream_push(StreamSlave *obj, uint8_t *buf, size_t size)
         uint16_t csum;
 
         tmp_csum = net_checksum_add(size - start_off,
-                                    (uint8_t *)buf + start_off);
+                                    buf + start_off);
         /* Accumulate the seed.  */
         tmp_csum += s->hdr[2] & 0xffff;