drm/i915/ttm: fix large buffer population trucation

ttm->num_pages is uint32_t which was causing very large buffers to
only populate a truncated size.

This fixes gem_create@create-clear igt test on large memory systems.

Fixes: 7ae03459 ("drm/i915/ttm: add tt shmem backend")
Signed-off-by: Robert Beckett <bob.beckett@collabora.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/20211210195005.2582884-1-bob.beckett@collabora.com

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

@@ -166,7 +166,7 @@ static int i915_ttm_tt_shmem_populate(struct ttm_device *bdev,
 	struct intel_memory_region *mr = i915->mm.regions[INTEL_MEMORY_SYSTEM];
 	struct i915_ttm_tt *i915_tt = container_of(ttm, typeof(*i915_tt), ttm);
 	const unsigned int max_segment = i915_sg_segment_size();
-	const size_t size = ttm->num_pages << PAGE_SHIFT;
+	const size_t size = (size_t)ttm->num_pages << PAGE_SHIFT;
 	struct file *filp = i915_tt->filp;
 	struct sgt_iter sgt_iter;
 	struct sg_table *st;