cachefiles: switch to kernel_write

__kernel_write doesn't take a sb_writers references, which we need here.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: David Howells <dhowells@redhat.com>

fs/cachefiles/rdwr.c

@@ -937,7 +937,7 @@ int cachefiles_write_page(struct fscache_storage *op, struct page *page)
 	}
 
 	data = kmap(page);
-	ret = __kernel_write(file, data, len, &pos);
+	ret = kernel_write(file, data, len, &pos);
 	kunmap(page);
 	fput(file);
 	if (ret != len)