USB Storage, add meaningful return value

This patch changes the "usb storage" command to return success if it
finds a USB storage device, otherwise it returns error.

Signed-off-by: Markus Klotzbuecher <mk@denx.de>
diff --git a/common/cmd_usb.c b/common/cmd_usb.c
index c6b17c2..ad32407 100644
--- a/common/cmd_usb.c
+++ b/common/cmd_usb.c
@@ -529,8 +529,7 @@
 	}
 
 	if (strncmp(argv[1], "stor", 4) == 0) {
-		usb_stor_info();
-		return 0;
+		return usb_stor_info();
 	}
 
 	if (strncmp(argv[1],"part",4) == 0) {