regmap: cache: Add extra parameter check in regcache_init

When num_reg_defaults > 0 but reg_defaults is NULL, there will be a
NULL pointer exception.

Current code has no such usage, but as additional hardening, also
check this to prevent any chance of crashing.

Signed-off-by: Schspa Shi <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

drivers/base/regmap/regcache.c

···
 		return -EINVAL;
 	}
 
+	if (config->num_reg_defaults && !config->reg_defaults) {
+		dev_err(map->dev,
+			"Register defaults number are set without the reg!\n");
+		return -EINVAL;
+	}
+
 	for (i = 0; i < config->num_reg_defaults; i++)
 		if (config->reg_defaults[i].reg % map->reg_stride)
 			return -EINVAL;