Mali: midgard: set "FMODE_UNSIGNED_OFFSET" bit in file flags of mali device file

According to commit "mmap: introduce sane default mmap limits"

Change-Id: I96bc78053c06fdeaef178662dda36770da867436
Signed-off-by: Zhen Chen <chenzhen@rock-chips.com>

drivers/gpu/arm/midgard/mali_kbase_core_linux.c

@@ -1154,6 +1154,7 @@ static int kbase_open(struct inode *inode, struct file *filp)
 	}
 
 	init_waitqueue_head(&kctx->event_queue);
+	filp->f_mode |= FMODE_UNSIGNED_OFFSET;
 	filp->private_data = kctx;
 	kctx->filp = filp;