rtlwifi: btcoexist: remove redundant variable fw_ps_state

Variable fw_ps_state is assigned a value but it is never read, hence
it is redundant and can be removed.

Cleans up clang warning:
drivers/net/wireless/realtek/rtlwifi/btcoexist/halbtcoutsrc.c:736:2:
warning: Value stored to 'fw_ps_state' is never read

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>