getevent: O_RDWR -> O_RDONLY | O_CLOEXEC

No need to open the device read write. Just open it read-only.

This is a partial redo of
https://android-review.googlesource.com/c/platform/system/core/+/334583
which was reverted in
https://android-review.googlesource.com/c/platform/system/core/+/342483

Bug: 30861057
Test: ran getevent, saw correct output, played with device
Change-Id: I426efd68f39dcd97d3ee23c13ed1a9ed96cb4c2e

toolbox/getevent.c

@@ -321,7 +321,7 @@ static int open_device(const char *device, int print_flags)
     char idstr[80];
     struct input_id id;
 
-    fd = open(device, O_RDWR);
+    fd = open(device, O_RDONLY | O_CLOEXEC);
     if(fd < 0) {
         if(print_flags & PRINT_DEVICE_ERRORS)
             fprintf(stderr, "could not open %s, %s\n", device, strerror(errno));