staging: rtl8188eu: simplify rtw_get_wireless_stats

Remove unnecessary temporary variables.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20210605165858.3175-5-martin@kaiser.cx


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