RDMA/core: Update kernel documentation for ib_create_named_qp()

Commit 66f57b871e ("RDMA/restrack: Support all QP types") extends
ib_create_qp() to a named ib_create_named_qp(), which takes the caller's
name as argument, but it did not add the new argument description to the
function's kerneldoc.

make htmldocs warns:

  ./drivers/infiniband/core/verbs.c:1206: warning: Function parameter or member 'caller' not described in 'ib_create_named_qp'

Add a description for this new argument based on the description of the
same argument in other related functions.

Fixes: 66f57b871e ("RDMA/restrack: Support all QP types")
Link: https://lore.kernel.org/r/20201207173255.13355-1-lukas.bulwahn@gmail.com
Signed-off-by: Lukas Bulwahn <lukas.bulwahn@gmail.com>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>

drivers/infiniband/core/verbs.c

@@ -1197,6 +1197,7 @@ static struct ib_qp *create_xrc_qp_user(struct ib_qp *qp,
  * @qp_init_attr: A list of initial attributes required to create the
  *   QP.  If QP creation succeeds, then the attributes are updated to
  *   the actual capabilities of the created QP.
+ * @caller: caller's build-time module name
  *
  * NOTE: for user qp use ib_create_qp_user with valid udata!
  */