sdcard: fix the 'maximum data transfer rate' to 25MHz

To comply with Spec v1.10 (and 2.00, 3.01):

. TRAN_SPEED

for current SD Memory Cards that field must be always 0_0110_010b (032h) which is
equal to 25MHz - the mandatory maximum operating frequency of SD Memory Card.
Signed-off-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: NAlistair Francis <alistair.francis@xilinx.com>
Message-id: 20180215221325.7611-4-f4bug@amsat.org
[PMM: fixed comment indent]
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>

hw/sd/sd.c

@@ -357,7 +357,7 @@ static void sd_set_csd(SDState *sd, uint64_t size)
         sd->csd[0] = 0x00;	/* CSD structure */
         sd->csd[1] = 0x26;	/* Data read access-time-1 */
         sd->csd[2] = 0x00;	/* Data read access-time-2 */
-        sd->csd[3] = 0x5a;	/* Max. data transfer rate */
+        sd->csd[3] = 0x32;      /* Max. data transfer rate: 25 MHz */
         sd->csd[4] = 0x5f;	/* Card Command Classes */
         sd->csd[5] = 0x50 |	/* Max. read data block length */
             HWBLOCK_SHIFT;