drm/i915/buddy: tweak 2big check

Otherwise we get -EINVAL, instead of the more useful -E2BIG if the
allocation doesn't fit within the pfn range, like with mappable lmem.
The hugepages selftest, for example, needs this to know if a smaller
size is needed.
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Reviewed-by: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Acked-by: Nirmoy Das <nirmoy.das@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220225145502.331818-6-matthew.auld@intel.com

drivers/gpu/drm/i915/i915_ttm_buddy_manager.c

@@ -82,7 +82,7 @@ static int i915_ttm_buddy_man_alloc(struct ttm_resource_manager *man,
 			lpfn = pages;
 	}
 
-	if (size > mm->size) {
+	if (size > lpfn << PAGE_SHIFT) {
 		err = -E2BIG;
 		goto err_free_res;
 	}