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

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

drivers/staging/rtl8723bs/core/rtw_xmit.c: In function update_attrib:
drivers/staging/rtl8723bs/core/rtw_xmit.c:680:7: warning: variable i set but not used [-Wunused-but-set-variable]

It is not used since commit 554c0a3a ("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/1570578905-95675-1-git-send-email-zhengbin13@huawei.com


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