[PATCH] replace deprecated vfs_read with kernel_read

See anbox/anbox#486 and related issue with ashmem and ZFS:
openzfs/spl#656

kernel/ashmem/ashmem.c

@@ -313,7 +313,7 @@ static ssize_t ashmem_read(struct file *file, char __user *buf,
 	 * be destroyed until all references to the file are dropped and
 	 * ashmem_release is called.
 	 */
-	ret = __vfs_read(asma->file, buf, len, pos);
+	ret = kernel_read(asma->file, buf, len, pos);
 	if (ret >= 0)
 		/** Update backing file pos, since f_ops->read() doesn't */
 		asma->file->f_pos = *pos;