rtl8xxxu: Rename rtl8723au_phy_iq_calibrate() to rtl8xxxu_gen1_phy_iq_calibrate()

All supported gen1 parts use the same phy_iq_calibrate() function
(unlike their gen2 counterparts). Rename the function to reflect this.

Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>