fuse: rework fuse_do_ioctl()

fuse_do_ioctl() already calculates the number of pages it's going to use. It is
stored in 'num_pages' variable. So the patch simply uses it for allocating
fuse_req.

Signed-off-by: Maxim Patlasov <mpatlasov@parallels.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
diff --git a/fs/fuse/file.c b/fs/fuse/file.c
index b997250..fdb5b33 100644
--- a/fs/fuse/file.c
+++ b/fs/fuse/file.c
@@ -1894,7 +1894,7 @@
 		num_pages++;
 	}
 
-	req = fuse_get_req(fc, FUSE_MAX_PAGES_PER_REQ);
+	req = fuse_get_req(fc, num_pages);
 	if (IS_ERR(req)) {
 		err = PTR_ERR(req);
 		req = NULL;