disk: part: Don't show redundant error message

Underlying API should already print some meaningful error message, so
this one is just brings more noise. E.g. we can see log like this:

    MMC: no card present
    ** Bad device mmc 0 **

Obviously, second error message is unwanted. Let's only print it in case
when DEBUG is defined to keep log short and clear.
Signed-off-by: NSam Protsenko <semen.protsenko@linaro.org>

disk/part.c

@@ -400,7 +400,7 @@ int blk_get_device_by_str(const char *ifname, const char *dev_hwpart_str,
 
 	*dev_desc = get_dev_hwpart(ifname, dev, hwpart);
 	if (!(*dev_desc) || ((*dev_desc)->type == DEV_TYPE_UNKNOWN)) {
-		printf("** Bad device %s %s **\n", ifname, dev_hwpart_str);
+		debug("** Bad device %s %s **\n", ifname, dev_hwpart_str);
 		dev = -ENOENT;
 		goto cleanup;
 	}