staging: r8188eu: smooth_rssi_data is not used

struct smooth_rssi_data is not used in this driver.
It can be removed.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20220226181457.1138035-2-martin@kaiser.cx


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>