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/mount_handler.cpp b/init/mount_handler.cpp
index 0e4e024..01abba8 100644
--- a/init/mount_handler.cpp
+++ b/init/mount_handler.cpp
@@ -116,7 +116,7 @@
     if (!fp_) PLOG(FATAL) << "Could not open /proc/mounts";
     auto result = epoll->RegisterHandler(
             fileno(fp_.get()), [this]() { this->MountHandlerFunction(); }, EPOLLERR | EPOLLPRI);
-    if (!result) LOG(FATAL) << result.error();
+    if (!result.ok()) LOG(FATAL) << result.error();
 }
 
 MountHandler::~MountHandler() {