ANDROID: binder: fix proc->tsk check.

Commit c4ea41ba ("binder: use group leader instead of open thread")'
was incomplete and didn't update a check in binder_mmap(), causing all
mmap() calls into the binder driver to fail.
Signed-off-by: Martijn Coenen <maco@android.com>
Tested-by: John Stultz <john.stultz@linaro.org>
Cc: stable <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/android/binder.c

@@ -3362,7 +3362,7 @@ static int binder_mmap(struct file *filp, struct vm_area_struct *vma)
 	const char *failure_string;
 	struct binder_buffer *buffer;
 
-	if (proc->tsk != current)
+	if (proc->tsk != current->group_leader)
 		return -EINVAL;
 
 	if ((vma->vm_end - vma->vm_start) > SZ_4M)