RDMA/netlink: Add __maybe_unused to static inline in C file

Like other commits in the tree add __maybe_unused to a static inline in a
C file because some clang compilers will complain about unused code:

>> drivers/infiniband/core/nldev.c:2543:1: warning: unused function '__chk_RDMA_NL_NLDEV'
MODULE_ALIAS_RDMA_NETLINK(RDMA_NL_NLDEV, 5);
^

Fixes: e3bf14bdc17a ("rdma: Autoload netlink client modules")
Link: https://lore.kernel.org/r/[e-mail]
Reported-by: kernel test robot <[e-mail]>
Signed-off-by: Leon Romanovsky <[e-mail]>
Signed-off-by: Jason Gunthorpe <[e-mail]>

include/rdma/rdma_netlink.h

···
  * constant as well and the compiler checks they are the same.
  */
 #define MODULE_ALIAS_RDMA_NETLINK(_index, _val)                                \
-	static inline void __chk_##_index(void)                                \
+	static inline void __maybe_unused __chk_##_index(void)                 \
 	{                                                                      \
 		BUILD_BUG_ON(_index != _val);                                  \
 	}                                                                      \