mmc: atmel-mci: fix oops in atmci_tasklet_func

In some cases, a NULL pointer dereference happens because data is NULL when
STATE_END_REQUEST case is reached in atmci_tasklet_func.

Cc: <stable@vger.kernel.org> # 3.9+
Signed-off-by: Rodolfo Giometti <giometti@enneenne.com>
Acked-by: Ludovic Desroches <ludovic.desroches@atmel.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Chris Ball <cjb@laptop.org>

drivers/mmc/host/atmel-mci.c

@@ -1810,12 +1810,14 @@ static void atmci_tasklet_func(unsigned long priv)
 			if (unlikely(status)) {
 				host->stop_transfer(host);
 				host->data = NULL;
-				if (status & ATMCI_DTOE) {
-					data->error = -ETIMEDOUT;
-				} else if (status & ATMCI_DCRCE) {
-					data->error = -EILSEQ;
-				} else {
-					data->error = -EIO;
+				if (data) {
+					if (status & ATMCI_DTOE) {
+						data->error = -ETIMEDOUT;
+					} else if (status & ATMCI_DCRCE) {
+						data->error = -EILSEQ;
+					} else {
+						data->error = -EIO;
+					}
 				}
 			}