staging/csr: Use kmemdup rather than duplicating its implementation

Found with coccicheck.
The semantic patch that makes this change is available
in scripts/coccinelle/api/memdup.cocci.
Signed-off-by: NPeter Huewe <peterhuewe@gmx.de>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/csr/drv.c

@@ -820,14 +820,14 @@ unifi_write(struct file *filp, const char *p, size_t len, loff_t *poff)
                     sig_id, signal_size);
 
 	/* Allocate a buffer for the signal */
-        signal_buf = kmalloc(signal_size, GFP_KERNEL);
+	signal_buf = kmemdup(bulkdata.d[0].os_data_ptr, signal_size,
+				GFP_KERNEL);
         if (!signal_buf) {
             unifi_net_data_free(priv, &bulkdata.d[0]);
             return -ENOMEM;
         }
 
         /* Get the signal from the os_data_ptr */
-        memcpy(signal_buf, bulkdata.d[0].os_data_ptr, signal_size);
         signal_buf[5] = (pcli->sender_id >> 8) & 0xff;
 
         if (signal_size < len) {