drm/i915: Fix one wrong caching mode enum usage

Commit a4d86249 ("drm/i915/gt: Provide a utility to create a scratch
buffer") mistakenly passed in uapi I915_CACHING_CACHED as argument to
i915_gem_object_set_cache_coherency(), which actually takes internal
enum i915_cache_level.

No functional issue since the value matches I915_CACHE_LLC (1 == 1), which
is the intended caching mode, but lets clean it up nevertheless.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Fixes: a4d86249 ("drm/i915/gt: Provide a utility to create a scratch buffer")
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Tejas Upadhyay <tejas.upadhyay@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230707125503.3965817-1-tvrtko.ursulin@linux.intel.com