IB/hns: Explicitly include linux/of.h

hns_roce_hw_v1.c uses DT interfaces but relies on implict inclusion of
linux/of.h which means that changes in other headers could break the
build, as happened in -next for arm64 today.  Add an explicit include.

Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Doug Ledford <dledford@redhat.com>