ANDROID: fix binder change in merge of 4.9.188

The 4.9.188 merge was missing the change to the
binder driver associated with the linux-4.9.y
commit 16903f1a5ba7 ("coredump: fix race condition
between mmget_not_zero()/get_task_mm() and core dumping").
It was left out because the android-4.9 binder
driver has been significantly refactored compared
to linux-4.9.y.

This patch applies the missing change from that
patch to the binder driver.

Change-Id: I803e558cb629fedff04b14e23ac9f83e98628ede
Fixes: d4fff2d0a879 ("Merge 4.9.188 into android-4.9")
Signed-off-by: Todd Kjos <tkjos@google.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
diff --git a/drivers/android/binder_alloc.c b/drivers/android/binder_alloc.c
index ce006af..da28422 100644
--- a/drivers/android/binder_alloc.c
+++ b/drivers/android/binder_alloc.c
@@ -219,6 +219,11 @@
 
 	if (mm) {
 		down_read(&mm->mmap_sem);
+		if (!mmget_still_valid(mm)) {
+			if (allocate == 0)
+				goto free_range;
+			goto err_no_vma;
+		}
 		vma = alloc->vma;
 	}