dma-buf: Include missing parentheses to documentation

The missing parentheses prevents the function to be rendered as a link
in the documentation. So, add the missing parentheses to the function on
the documentation.
Signed-off-by: Maíra Canal <mcanal@igalia.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Maíra Canal <mairacanal@riseup.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20230223121909.149980-1-mcanal@igalia.com

drivers/dma-buf/dma-buf.c

@@ -828,7 +828,7 @@ static struct sg_table * __map_dma_buf(struct dma_buf_attachment *attach,
  *     - dma_buf_attach()
  *     - dma_buf_dynamic_attach()
  *     - dma_buf_detach()
- *     - dma_buf_export(
+ *     - dma_buf_export()
  *     - dma_buf_fd()
  *     - dma_buf_get()
  *     - dma_buf_put()