drm/i915/ttm: fix sparse warning

Sparse complains with:

drivers/gpu/drm/i915/gem/i915_gem_ttm.c:1066:21: sparse:
	expected restricted vm_fault_t [assigned] [usertype] ret
drivers/gpu/drm/i915/gem/i915_gem_ttm.c:1066:21: sparse: got int

Fixes: 516198d3 ("drm/i915: audit bo->resource usage v3")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230130101230.25347-1-matthew.auld@intel.comReviewed-by: Nirmoy Das <nirmoy.das@intel.com>
Acked-by: Christian König <ckoenig.leichtzumerken@gmail.com>
Signed-off-by: Christian König <christian.koenig@amd.com>

drivers/gpu/drm/i915/gem/i915_gem_ttm.c

@@ -1067,11 +1067,12 @@ static vm_fault_t vm_fault_ttm(struct vm_fault *vmf)
 			.interruptible = true,
 			.no_wait_gpu = true, /* should be idle already */
 		};
+		int err;
 
 		GEM_BUG_ON(!bo->ttm || !(bo->ttm->page_flags & TTM_TT_FLAG_SWAPPED));
 
-		ret = ttm_bo_validate(bo, i915_ttm_sys_placement(), &ctx);
-		if (ret) {
+		err = ttm_bo_validate(bo, i915_ttm_sys_placement(), &ctx);
+		if (err) {
 			dma_resv_unlock(bo->base.resv);
 			return VM_FAULT_SIGBUS;
 		}