rtw89: change value assignment style of rtw89_mac_cfg_gnt()

Use if() style would be clear than "? :", because the else cases are
always 0. The read val from rtw89_mac_read_lte() isn't used, so remove
this statement.

Signed-off-by: Ping-Ke Shih <pkshih@realtek.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://lore.kernel.org/r/20220317055543.40514-11-pkshih@realtek.com