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: e3bf14bd ("rdma: Autoload netlink client modules")
Link: https://lore.kernel.org/r/4a8101919b765e01d7fde6f27fd572c958deeb4a.1636267207.git.leonro@nvidia.comReported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

include/rdma/rdma_netlink.h

@@ -30,7 +30,7 @@ enum rdma_nl_flags {
  * 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);                                  \
 	}                                                                      \