rtw88: Make some symbols static

Fix sparse warnings:

drivers/net/wireless/realtek/rtw88/phy.c:851:4: warning: symbol 'rtw_cck_size' was not declared. Should it be static?
drivers/net/wireless/realtek/rtw88/phy.c:852:4: warning: symbol 'rtw_ofdm_size' was not declared. Should it be static?
drivers/net/wireless/realtek/rtw88/phy.c:853:4: warning: symbol 'rtw_ht_1s_size' was not declared. Should it be static?
drivers/net/wireless/realtek/rtw88/phy.c:854:4: warning: symbol 'rtw_ht_2s_size' was not declared. Should it be static?
drivers/net/wireless/realtek/rtw88/phy.c:855:4: warning: symbol 'rtw_vht_1s_size' was not declared. Should it be static?
drivers/net/wireless/realtek/rtw88/phy.c:856:4: warning: symbol 'rtw_vht_2s_size' was not declared. Should it be static?
drivers/net/wireless/realtek/rtw88/fw.c:11:6: warning: symbol 'rtw_fw_c2h_cmd_handle_ext' was not declared. Should it be static?
drivers/net/wireless/realtek/rtw88/fw.c:50:6: warning: symbol 'rtw_fw_send_h2c_command' 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>