drm/i915/gt: Remove const from struct i915_wa list allocation

In preparation for making the kmalloc family of allocators type aware,
we need to make sure that the returned type from the allocation matches
the type of the variable being assigned. (Before, the allocator would
always return "void *", which can be implicitly cast to any pointer type.)

The assigned type is "struct i915_wa *". The returned type, while
technically matching, will be const qualified. As there is no general
way to remove const qualifiers, adjust the allocation type to match
the assignment.

Signed-off-by: Kees Cook <kees@kernel.org>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Signed-off-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://lore.kernel.org/r/20250426061357.work.749-kees@kernel.org