staging: rtl8187se: use memdup_user to simplify code

This patch fixes the following coccinelle warning to use memdup_user
rather than duplicating its implementation:

drivers/staging/rtl8187se/ieee80211/ieee80211_softmac.c:2947:9-16: WARNING opportunity for memdup_user
Signed-off-by: Teodora Baluta <teobaluta@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/rtl8187se/ieee80211/ieee80211_softmac.c

@@ -2944,14 +2944,9 @@ int ieee80211_wpa_supplicant_ioctl(struct ieee80211_device *ieee, struct iw_poin
 		goto out;
 	}
 
-	param = kmalloc(p->length, GFP_KERNEL);
-	if (param == NULL){
-		ret = -ENOMEM;
-		goto out;
-	}
-	if (copy_from_user(param, p->pointer, p->length)) {
-		kfree(param);
-		ret = -EFAULT;
+	param = memdup_user(p->pointer, p->length);
+	if (IS_ERR(param)) {
+		ret = PTR_ERR(param);
 		goto out;
 	}