rtw88: Make two functions static

Fix sparse warnings:

drivers/net/wireless/realtek/rtw88/fw.c:633:4: warning:
 symbol 'rtw_get_rsvd_page_probe_req_location' was not declared. Should it be static?
drivers/net/wireless/realtek/rtw88/fw.c:650:5: warning:
 symbol 'rtw_get_rsvd_page_probe_req_size' was not declared. Should it be static?

Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200328030524.16032-1-yuehaibing@huawei.com