staging: rtl8192u: Remove unused code

Below return statement dm_send_rssi_tofw
function has dead code.

This patch removes dead code from dm_send_rssi_tofw.

This was detected by smatch.

Signed-off-by: Tapasweni Pathak <tapaswenipathak@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>