intel: Add missing #include <time.h>

Commit 006c1a3c65 introduced a call to
clock_gettime, but failed to include <time.h>, breaking the build in
some cases.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>

src/mesa/drivers/dri/intel/intel_screen.c

@@ -26,6 +26,7 @@
  **************************************************************************/
 
 #include <errno.h>
+#include <time.h>
 #include "main/glheader.h"
 #include "main/context.h"
 #include "main/framebuffer.h"