RDMA/uverbs: Import DMA-BUF module in uverbs_std_types_dmabuf file

Fix the following compilation error:

ERROR: modpost: module ib_uverbs uses symbol dma_buf_move_notify
	from namespace DMA_BUF, but does not import it.

Fixes: 0ac6f4056c4a ("RDMA/uverbs: Add DMABUF object type and operations")
Signed-off-by: Leon Romanovsky <leonro@nvidia.com>

drivers/infiniband/core/uverbs_std_types_dmabuf.c

diff --git a/drivers/infiniband/core/uverbs_std_types_dmabuf.c b/drivers/infiniband/core/uverbs_std_types_dmabuf.c
index dfdfcd1..4a7f8b6 100644
--- a/drivers/infiniband/core/uverbs_std_types_dmabuf.c
+++ b/drivers/infiniband/core/uverbs_std_types_dmabuf.c
@@ -10,6 +10,8 @@
 #include "rdma_core.h"
 #include "uverbs.h"
 
+MODULE_IMPORT_NS("DMA_BUF");
+
 static int uverbs_dmabuf_attach(struct dma_buf *dmabuf,
 				struct dma_buf_attachment *attachment)
 {