ASoC: Check that WM8996 FLL started even if we don't have the IRQ

We can directly read the FLL lock status on WM8996 so even if we don't
have an interrupt wired up we can still verify that the FLL started
successfully.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Liam Girdwood <lrg@ti.com>