RDMA/uverbs: Fix typo in string concatenation macro

Update UVERBS_OBJECT() macro to properly concatenate the object name.

Fixes: e502a864 ("IB/core: Introduce DECLARE_UVERBS_GLOBAL_METHODS")
Signed-off-by: Leon Romanovsky <leonro@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>