fastboot: get rid of manual transport memory management

Existing code has transport memory leaks. Use smart pointers
for transport to get rid of those cases and manual memory
management

Test: atest fastboot_test
Test: manually checked transport isn't leaking anymore
Bug: 296629925
Change-Id: Ifdf162d5084f61ae5c1d2b56a897464af58100da
Signed-off-by: Dmitrii Merkurev <dimorinny@google.com>
diff --git a/fastboot/usb_linux.cpp b/fastboot/usb_linux.cpp
index 964488c..37bb304 100644
--- a/fastboot/usb_linux.cpp
+++ b/fastboot/usb_linux.cpp
@@ -503,9 +503,15 @@
     return 0;
 }
 
-UsbTransport* usb_open(ifc_match_func callback, uint32_t timeout_ms) {
+std::unique_ptr<UsbTransport> usb_open(ifc_match_func callback, uint32_t timeout_ms) {
+    std::unique_ptr<UsbTransport> result;
     std::unique_ptr<usb_handle> handle = find_usb_device("/sys/bus/usb/devices", callback);
-    return handle ? new LinuxUsbTransport(std::move(handle), timeout_ms) : nullptr;
+
+    if (handle) {
+        result = std::make_unique<LinuxUsbTransport>(std::move(handle), timeout_ms);
+    }
+
+    return result;
 }
 
 /* Wait for the system to notice the device is gone, so that a subsequent