staging: rtl8723bs: Remove set but not used variable 'adapter'

staging: rtl8723bs: Remove set but not used variable 'adapter'

Fixes gcc '-Wunused-but-set-variable' warning:

drivers/staging/rtl8723bs/core/rtw_mlme.c: In function rtw_select_roaming_candidate:
drivers/staging/rtl8723bs/core/rtw_mlme.c:2007:18: warning: variable adapter set but not used [-Wunused-but-set-variable]

It is not used since commit 88a1abb19b1d ("staging:
Add rtl8723bs sdio wifi driver")

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: zhengbin <zhengbin13@huawei.com>
Link: https://lore.kernel.org/r/1570352999-45790-6-git-send-email-zhengbin13@huawei.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>