keychords.cpp: O_RDWR -> O_RDONLY

The keycodes functionality in init only needs to read key events. It
doesn't need to inject key events. A read-only file descriptor is
perfectly sufficient.

Test: pressing volume-up/volume-down/power still generates a bugreport
Change-Id: Iecbf21c544914334006ac6258c03df390f417e80
diff --git a/init/keychords.cpp b/init/keychords.cpp
index 1af06dd..b8c1cfd 100644
--- a/init/keychords.cpp
+++ b/init/keychords.cpp
@@ -192,7 +192,7 @@
 
 void Keychords::GeteventOpenDevice(const std::string& device) {
     if (registration_.count(device)) return;
-    auto fd = TEMP_FAILURE_RETRY(::open(device.c_str(), O_RDWR | O_CLOEXEC));
+    auto fd = TEMP_FAILURE_RETRY(::open(device.c_str(), O_RDONLY | O_CLOEXEC));
     if (fd == -1) {
         PLOG(ERROR) << "Can not open " << device;
         return;