IB/hfi1: Get rid of a warning

The right markup for a variable is @foo, and not @foo[].

Using a wrong markup caused this warning:

	./drivers/infiniband/ulp/opa_vnic/opa_vnic_encap.h:243: WARNING: Inline strong start-string without end-string.

Link: https://lore.kernel.org/r/9dce702510505556d75a13d9641e09218a4b4a65.1584456635.git.mchehab+huawei@kernel.org
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>