IB/core: const'ify inbuf in struct ib_udata

Userspace input buffer is not modified by kernel, so it can be 'const'.

This is also a prerequisite to remove the implicit cast
from INIT_UDATA().

Link: http://marc.info/?i=cover.1386798254.git.ydroneaud@opteya.com>
Signed-off-by: Yann Droneaud <ydroneaud@opteya.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>
diff --git a/drivers/infiniband/core/uverbs.h b/drivers/infiniband/core/uverbs.h
index bdc842e..9879568 100644
--- a/drivers/infiniband/core/uverbs.h
+++ b/drivers/infiniband/core/uverbs.h
@@ -49,7 +49,7 @@
 
 #define INIT_UDATA(udata, ibuf, obuf, ilen, olen)			\
 	do {								\
-		(udata)->inbuf  = (void __user *) (ibuf);		\
+		(udata)->inbuf  = (const void __user *) (ibuf);		\
 		(udata)->outbuf = (void __user *) (obuf);		\
 		(udata)->inlen  = (ilen);				\
 		(udata)->outlen = (olen);				\