IB/ipath: Remove reference to dev->class_dev

IB/ipath: Remove reference to dev->class_dev

Commit 124b4dcb ("IB/ipath: add calls to new 7220 code and enable in
build") inadvertently added core to set dev->class_dev.dev back into
ib_ipath.  This is completely redundant since commit 1912ffbb ("IB: Set
class_dev->dev in core for nice device symlink"), which removed
class_dev setting from low-level drivers, and also will break the build
when class_dev is removed completely from struct ib_device.

Signed-off-by: Roland Dreier <rolandd@cisco.com>