staging: rtl8188eu: make rtw_free_recvframe return void

None of the callers checks the return value of rtw_free_recvframe.

Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Link: https://lore.kernel.org/r/20210605165858.3175-4-martin@kaiser.cx


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