test: Avoid random numbers in dm_test_devm_regmap()

There is no good reason to use a sequence from rand() here. We may as well
invent our own sequence.

This should molify Coverity which does not use rand() being used.
Signed-off-by: NSimon Glass <sjg@chromium.org>
Reported-by: Coverity (CID: 312949)

test/dm/regmap.c

@@ -306,9 +306,8 @@ static int dm_test_devm_regmap(struct unit_test_state *uts)
 					      &dev));
 	priv = dev_get_priv(dev);
 
-	srand(get_ticks() + rand());
 	for (i = 0; i < REGMAP_TEST_BUF_SZ; i++) {
-		pattern[i] = rand();
+		pattern[i] = i * 0x87654321;
 		ut_assertok(regmap_write(priv->cfg_regmap, i, pattern[i]));
 	}
 	for (i = 0; i < REGMAP_TEST_BUF_SZ; i++) {