net/9p: Add __force to cast of __user pointer

A recent commit that removed unnecessary casts of pointers
to the same type uncovered a missing __force cast.

Add it.

Reported by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/9p/client.c b/net/9p/client.c
index 5cbea90..8260f13 100644
--- a/net/9p/client.c
+++ b/net/9p/client.c
@@ -1548,7 +1548,7 @@
 			kernel_buf = 1;
 			indata = data;
 		} else
-			indata = udata;
+			indata = (__force char *)udata;
 		/*
 		 * response header len is 11
 		 * PDU Header(7) + IO Size (4)