cachefiles_write_page(): switch to __kernel_write()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/read_write.c b/fs/read_write.c
index 009d854..7d9318c 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -513,6 +513,8 @@
 	return ret;
 }
 
+EXPORT_SYMBOL(__kernel_write);
+
 ssize_t vfs_write(struct file *file, const char __user *buf, size_t count, loff_t *pos)
 {
 	ssize_t ret;