pwm: meson: Fix axg ao mux parents

This fix is basically the same as 9bce02ef ("pwm: meson: Fix the
G12A AO clock parents order"). Vendor driver referenced there has
xtal as first parent also for axg ao. In addition fix the name
of the aoclk81 clock. Apparently name aoclk81 as used by the vendor
driver was changed when mainlining the axg clock driver.

Fixes: bccaa3f9 ("pwm: meson: Add clock source configuration for Meson-AXG")
Cc: stable@vger.kernel.org
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Reviewed-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>