drm/i915: properly init lockdep class

The code has an ifdef and uses two functions to either init the bare
spinlock or init it and set a lock-class. It is possible to do the same
thing without an ifdef.
With this patch (in debug case) we first use the "default" lock class
which is later overwritten to the supplied one. Without lockdep the set
name/class function vanishes.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171214131009.7479-1-joonas.lahtinen@linux.intel.com
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>