fs: cifs: Remove repeated struct declaration

struct cifs_writedata is declared twice.
One is declared at 209th line.
And struct cifs_writedata is defined blew.
The declaration hear is not needed. Remove the duplicate.
Signed-off-by: Wan Jiabing <wanjiabing@vivo.com>
Signed-off-by: Steve French <stfrench@microsoft.com>

fs/cifs/cifsglob.h

@@ -1314,8 +1314,6 @@ struct cifs_readdata {
 	struct page			**pages;
 };
 
-struct cifs_writedata;
-
 /* asynchronous write support */
 struct cifs_writedata {
 	struct kref			refcount;