staging: rtl8723bs: core: rtw_ap: fix Unneeded variable: "ret". Return "0"

Function "rtw_sta_flush" always returns 0 value.
So change return type of rtw_sta_flush from int to void.

Same thing applies for rtw_hostapd_sta_flush

Signed-off-by: Hariprasad Kelam <hariprasad.kelam@gmail.com>
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Changes v2 -
       change return type of rtw_sta_flush
Changes v3 -
       fix indentaion issue
Changes v4 -
       prepare patch on linux-next
Changes v5 -
      cleanup subject and commit message

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