sd/sdhci.c: Only reset data_count on new commands

The data_count variable was being reset on every transfer, including
DMA transfer resumptions. This is incorrect, it should only be set
on a new command.

Manifests as a bug when using ADMA and there is a timer delay between
ADMA frames where the fifo is left in a non empty state.

Signed-off-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Reviewed-by: Igor Mitsyanko <i.mitsyanko@gmail.com>
Message-id: 15a98609cc32315211b0963091a8efd67522e160.1369370934.git.peter.crosthwaite@xilinx.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>

hw/sd/sdhci.c

@@ -260,6 +260,7 @@ static void sdhci_send_command(SDHCIState *s)
     sdhci_update_irq(s);
 
     if (s->blksize && (s->cmdreg & SDHC_CMD_DATA_PRESENT)) {
+        s->data_count = 0;
         sdhci_do_data_transfer(s);
     }
 }
@@ -773,7 +774,6 @@ static void sdhci_do_adma(SDHCIState *s)
 static void sdhci_data_transfer(SDHCIState *s)
 {
     SDHCIClass *k = SDHCI_GET_CLASS(s);
-    s->data_count = 0;
 
     if (s->trnmod & SDHC_TRNS_DMA) {
         switch (SDHC_DMA_TYPE(s->hostctl)) {