hw/sd/sdcard: Constify sd_crc*()'s message argument

CRC functions don't modify the buffer argument,
make it const.

Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20200630133912.9428-14-f4bug@amsat.org>

hw/sd/sd.c

@@ -254,11 +254,11 @@ static const int sd_cmd_class[SDMMC_CMD_MAX] = {
     7,  7, 10,  7,  9,  9,  9,  8,  8, 10,  8,  8,  8,  8,  8,  8,
 };
 
-static uint8_t sd_crc7(void *message, size_t width)
+static uint8_t sd_crc7(const void *message, size_t width)
 {
     int i, bit;
     uint8_t shift_reg = 0x00;
-    uint8_t *msg = (uint8_t *) message;
+    const uint8_t *msg = (const uint8_t *)message;
 
     for (i = 0; i < width; i ++, msg ++)
         for (bit = 7; bit >= 0; bit --) {
@@ -270,11 +270,11 @@ static uint8_t sd_crc7(void *message, size_t width)
     return shift_reg;
 }
 
-static uint16_t sd_crc16(void *message, size_t width)
+static uint16_t sd_crc16(const void *message, size_t width)
 {
     int i, bit;
     uint16_t shift_reg = 0x0000;
-    uint16_t *msg = (uint16_t *) message;
+    const uint16_t *msg = (const uint16_t *)message;
     width <<= 1;
 
     for (i = 0; i < width; i ++, msg ++)