pwm: meson: Fix g12a ao clk81 name

Fix the name of the aoclk81 clock. Apparently name aoclk81 as used by
the vendor driver was changed when mainlining the g12a clock driver.

Fixes: f41efceb ("pwm: meson: Add clock source configuration for Meson G12A")
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>