USB: storage: ums-realtek: Update module parameter description for auto_delink_en

The option named "auto_delink_en" is a bit misleading, as setting it to
false doesn't really disable auto-delink but let auto-delink be firmware
controlled.

Update the description to reflect the real usage of this parameter.

Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20190827173450.13572-1-kai.heng.feng@canonical.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>