usb: core: Copy parameter string correctly and remove superfluous null check

strsep() slices string, so the string gets copied by
param_set_copystring() at the end of quirks_param_set() is not the
original value.
Fix that by calling param_set_copystring() earlier.

The null check for val is unnecessary, the caller of quirks_param_set()
does not pass null string.
Remove the superfluous null check. This is found by Smatch.

Fixes: 027bd6cafd9a ("usb: core: Add "quirks" parameter for usbcore")
Cc: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/core/quirks.c

@@ -31,10 +31,15 @@ static int quirks_param_set(const char *val, const struct kernel_param *kp)
 	u16 vid, pid;
 	u32 flags;
 	size_t i;
+	int err;
+
+	err = param_set_copystring(val, kp);
+	if (err)
+		return err;
 
 	mutex_lock(&quirk_mutex);
 
-	if (!val || !*val) {
+	if (!*val) {
 		quirk_count = 0;
 		kfree(quirk_list);
 		quirk_list = NULL;
@@ -133,7 +138,7 @@ static int quirks_param_set(const char *val, const struct kernel_param *kp)
 unlock:
 	mutex_unlock(&quirk_mutex);
 
-	return param_set_copystring(val, kp);
+	return 0;
 }
 
 static const struct kernel_param_ops quirks_param_ops = {