atmel: at76c50x: use DEFINE_MUTEX() for mutex lock

mutex lock can be initialized automatically with DEFINE_MUTEX()
rather than explicitly calling mutex_init().
Signed-off-by: Zheng Yongjun <zhengyongjun3@huawei.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20201224132456.31341-1-zhengyongjun3@huawei.com

drivers/net/wireless/atmel/at76c50x-usb.c

@@ -101,7 +101,7 @@ do {									\
 static uint at76_debug = DBG_DEFAULTS;
 
 /* Protect against concurrent firmware loading and parsing */
-static struct mutex fw_mutex;
+static DEFINE_MUTEX(fw_mutex);
 
 static struct fwentry firmwares[] = {
 	[0] = { "" },
@@ -2572,8 +2572,6 @@ static int __init at76_mod_init(void)
 
 	printk(KERN_INFO DRIVER_DESC " " DRIVER_VERSION " loading\n");
 
-	mutex_init(&fw_mutex);
-
 	/* register this driver with the USB subsystem */
 	result = usb_register(&at76_driver);
 	if (result < 0)