Minor clock_getcpuclockid optimization.

Don't ask the kernel to copy data to userspace if we don't need it.
(Noticed while cleaning up sysconf to not call clock_getres.)

Change-Id: Icc0f7559775b8a2dcefe638ce831d06b75d67122

libc/bionic/clock_getcpuclockid.cpp

@@ -40,8 +40,7 @@ int clock_getcpuclockid(pid_t pid, clockid_t* clockid) {
   result |= 2;
   // Bit 2: thread (set) or process (clear). Bit 2 already 0.
 
-  timespec ts;
-  if (clock_getres(result, &ts) == -1) {
+  if (clock_getres(result, nullptr) == -1) {
     return ESRCH;
   }