test: firmware_class: use kstrndup() where appropriate

We're essentially just doing an open-coded kstrndup(). The only
differences are with what happens after the first '\0' character, but
request_firmware() doesn't care about that.
Suggested-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Signed-off-by: Shuah Khan <shuahkh@osg.samsung.com>

lib/test_firmware.c

@@ -54,10 +54,9 @@ static ssize_t trigger_request_store(struct device *dev,
 	int rc;
 	char *name;
 
-	name = kzalloc(count + 1, GFP_KERNEL);
+	name = kstrndup(buf, count, GFP_KERNEL);
 	if (!name)
 		return -ENOSPC;
-	memcpy(name, buf, count);
 
 	pr_info("loading '%s'\n", name);