Convert system/core to Result::ok()

No functionality changes, this is a mechanical cleanup.

Test: m
Test: cd system/core && atest
Change-Id: Ifdaa3ce1947ed578f656d5a446978726eb416c36
diff --git a/init/firmware_handler.cpp b/init/firmware_handler.cpp
index 1dce2d5..dff7b69 100644
--- a/init/firmware_handler.cpp
+++ b/init/firmware_handler.cpp
@@ -165,7 +165,7 @@
 
             auto result =
                     RunExternalHandler(external_handler.handler_path, external_handler.uid, uevent);
-            if (!result) {
+            if (!result.ok()) {
                 LOG(ERROR) << "Using default firmware; External firmware handler failed: "
                            << result.error();
                 return uevent.firmware;