staging: rtl8188eu: Refactoring struct ndis_802_11_ssid from CamelCase to correct code style.

rtl8188eu uses CamelCase for many struct members.
Refactors the ndis_802_11_ssid members Ssid and SsidLength to keep correct code style.
Issue found by checkpatch.

Signed-off-by: Florian Büstgens <flbue@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>