Add the missing #include of <functional>.

For the use of std::function and std::bind. They were relying on the
transitive inclusion from <minui/minui.h>.

Test: mmma bootable/recovery
Change-Id: Ia138e1cbdd035b11d6cdca9e16c5591303b6ee13

minui/events.cpp

@@ -24,6 +24,8 @@
 #include <sys/ioctl.h>
 #include <unistd.h>
 
+#include <functional>
+
 #include "minui/minui.h"
 
 #define MAX_DEVICES 16

ui.cpp

@@ -30,6 +30,7 @@
 #include <time.h>
 #include <unistd.h>
 
+#include <functional>
 #include <string>
 
 #include <android-base/file.h>