drm/i915: don't leak lmem mapping in vma_evict

Don't leak lmem mapping in vma_evict, move __i915_vma_iounmap outside
i915_vma_is_map_and_fenceable.

Signed-off-by: Juha-Pekka Heikkila <juhapekka.heikkila@gmail.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220610121205.29645-3-juhapekka.heikkila@gmail.com