ANDROID: fix kernelci build-break in lowmemorykiller

<linux/poll.h> was not included by lowmemorykiller.c
resulting in a kernelci build-break due to no definition
for 'poll_table'.

Fixes: 941128efa146c ("ANDROID: Communicates LMK events to
userland where they can be logged")
Signed-off-by: Todd Kjos <tkjos@google.com>

Change-Id: I5fb2d1d8f6e5afbdd00fbf017df37ec2e8b9ff9e

drivers/staging/android/lowmemorykiller.c

@@ -45,6 +45,7 @@
 #include <linux/circ_buf.h>
 #include <linux/proc_fs.h>
 #include <linux/slab.h>
+#include <linux/poll.h>
 
 #define CREATE_TRACE_POINTS
 #include "trace/lowmemorykiller.h"