cifs: use a flexarray in cifs_writedata

The cifs_writedata code uses a single element trailing array, which
just adds unneeded complexity. Use a flexarray instead.
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Reviewed-by: Pavel Shilovsky <piastry@etersoft.ru>
Signed-off-by: Steve French <smfrench@gmail.com>

fs/cifs/cifsglob.h

@@ -1068,7 +1068,7 @@ struct cifs_writedata {
 	unsigned int			pagesz;
 	unsigned int			tailsz;
 	unsigned int			nr_pages;
-	struct page			*pages[1];
+	struct page			*pages[];
 };
 
 /*

fs/cifs/cifssmb.c

@@ -1962,15 +1962,9 @@ cifs_writedata_alloc(unsigned int nr_pages, work_func_t complete)
 {
 	struct cifs_writedata *wdata;
 
-	/* this would overflow */
-	if (nr_pages == 0) {
-		cifs_dbg(VFS, "%s: called with nr_pages == 0!\n", __func__);
-		return NULL;
-	}
-
 	/* writedata + number of page pointers */
 	wdata = kzalloc(sizeof(*wdata) +
-			sizeof(struct page *) * (nr_pages - 1), GFP_NOFS);
+			sizeof(struct page *) * nr_pages, GFP_NOFS);
 	if (wdata != NULL) {
 		kref_init(&wdata->refcount);
 		INIT_LIST_HEAD(&wdata->list);