cifs: allocate kvec array for cifs_readdata as a separate allocation

Eventually, we're going to want to append a list of pages to
cifs_readdata instead of a list of kvecs. To prepare for that, turn
the kvec array allocation into a separate one and just keep a
pointer to it in the readdata.

Signed-off-by: Jeff Layton <jlayton@redhat.com>
diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
index cc70ac0..737289b 100644
--- a/fs/cifs/cifsglob.h
+++ b/fs/cifs/cifsglob.h
@@ -982,7 +982,7 @@
 	int (*marshal_iov) (struct cifs_readdata *rdata,
 			    unsigned int remaining);
 	unsigned int			nr_iov;
-	struct kvec			iov[1];
+	struct kvec			*iov;
 };
 
 struct cifs_writedata;