drm/i915/selftests: Tidy prng constructor for client blits

Since we only initialise the prng once within the scope of the selftest,
we can use the default initialiser.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20201202130406.18461-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gem/selftests/i915_gem_client_blt.c

@@ -20,13 +20,11 @@ static int __igt_client_fill(struct intel_engine_cs *engine)
 {
 	struct intel_context *ce = engine->kernel_context;
 	struct drm_i915_gem_object *obj;
-	struct rnd_state prng;
+	I915_RND_STATE(prng);
 	IGT_TIMEOUT(end);
 	u32 *vaddr;
 	int err = 0;
 
-	prandom_seed_state(&prng, i915_selftest.random_seed);
-
 	intel_engine_pm_get(engine);
 	do {
 		const u32 max_block_size = S16_MAX * PAGE_SIZE;