drm/i915: Eliminate superfluous i915_ggtt_view_rotated

It is only being used to clear a struct and set the type, after which it
is overwritten. Since we no longer check the unset bits of the union,
skipping the clear is permissible.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170114002827.31315-6-chris@chris-wilson.co.uk