rtlwifi: remove set but not used variable 'cmd_seq'

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

drivers/net/wireless/realtek/rtlwifi/base.c: In function 'rtl_c2h_content_parsing':
drivers/net/wireless/realtek/rtlwifi/base.c:2313:13: warning:
 variable 'cmd_seq' set but not used [-Wunused-but-set-variable]

Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Acked-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>