Don't rely on transitively included headers

One must explicitly include what it need.
time.h for clock_gettime

Bug: 37629934
Test: build
Merged-In: I992eac637f373b204aa161b0b26f5563e952c27e
Change-Id: I992eac637f373b204aa161b0b26f5563e952c27e
diff --git a/libutils/SystemClock.cpp b/libutils/SystemClock.cpp
index 28fc351..73ec1be 100644
--- a/libutils/SystemClock.cpp
+++ b/libutils/SystemClock.cpp
@@ -23,9 +23,9 @@
 
 #include <utils/SystemClock.h>
 
-#include <sys/time.h>
 #include <string.h>
 #include <errno.h>
+#include <time.h>
 
 #include <cutils/compiler.h>