acct: check FMODE_CAN_WRITE

it's not calling ->write() directly anymore.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/kernel/acct.c b/kernel/acct.c
index e6c10d1a..74963d1 100644
--- a/kernel/acct.c
+++ b/kernel/acct.c
@@ -213,7 +213,7 @@
 		return -EACCES;
 	}
 
-	if (!file->f_op->write) {
+	if (!(file->f_mode & FMODE_CAN_WRITE)) {
 		kfree(acct);
 		filp_close(file, NULL);
 		return -EIO;