main: Try cold flash again only if it returns -EAGAIN

src/main.c

@@ -781,9 +781,12 @@ int main(int argc, char **argv) {
 				usb_close_device(usb_dev);
 				usb_dev = NULL;
 
-				if ( ret != 0 )
+				if ( ret != -EAGAIN )
 					continue;
 
+				if ( ret != 0 )
+					goto clean;
+
 				if ( dev_flash ) {
 					dev_cold_flash = 0;
 					continue;