cmd: sata: add null pointer check for dev

Calling sata_scan() with a null pointer probably won't make much sense.

Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/cmd/sata.c b/cmd/sata.c
index 6d62ba8..a73cc54 100644
--- a/cmd/sata.c
+++ b/cmd/sata.c
@@ -60,6 +60,10 @@
 		printf("Cannot probe SATA device %d (err=%d)\n", devnum, rc);
 		return CMD_RET_FAILURE;
 	}
+	if (!dev) {
+		printf("No SATA device found!\n");
+		return CMD_RET_FAILURE;
+	}
 	rc = sata_scan(dev);
 	if (rc) {
 		printf("Cannot scan SATA device %d (err=%d)\n", devnum, rc);