staging: rtl8192e: GetTs Fix invalid TID 7 warning.

TID 7 is a valid value for QoS IEEE 802.11e.

The switch statement that follows states 7 is valid.

Remove function IsACValid and use the default case to filter
invalid TIDs.

Signed-off-by: Malcolm Priestley <tvboxspy@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>